18 November 2018 at 4:37 pm #574183
Wanting to invest in an off the shelf, and easy to use refractor, mainly to study the planets, and the occasional deep sky. I live in a first floor flat and the scope needs to be potable up a flight of stairs without casing a hernia, or worse! I’ve been looking at the Bresser range, and the 2 scopes that interest me are the Bresser Messier series, the 102mm F/13 and the 127mm F/9.5. Does anybody have any experience using any one of these 2 ‘scopes? I’d be interested in anybody’s opinion as with regard to their general quality and how much better (or worse maybe) the longer focus 102mm model compares with the larger aperture, but shorter focus 127mm model. In my book, longer focus refractors of a certain price range should perform better on diffraction limited objects, such as the planets. All opinions welcome, many thanks in anticipation.19 November 2018 at 10:14 am #580257Paul LeylandParticipant
Personally I’d go for the aperture if it’s within your budgetary and mechanical limitations. Most of the time the image will be seeing limited but the resolution of the larger will be better than the smaller in the brief intervals when the atmosphere in front of your telescope is steady. The extra light grasp will be invaluable if your tastes change and deep sky becomes more important, or if you branch out into fields such as VS and cometary observing.
As for focal length, note that 13*102 = 1326 and 9.5*127 = 1206.5 so the longer focal length is only 10% greater than the shorter.
Added in edit: (127/102)^2 = 1.55, so the light grasp is 55% greater, or roughly half a magnitude.19 November 2018 at 2:01 pm #580258
Thanks for that Paul, a very helpful and intelligent reply. I hadn’t quite looked at it in that light (pun not intended!) as I’m just a bit wary of anything of shorter f/ratio than F/11 on a 2 element refractor. Ideally it would be great to test them side by side, but that would be a rare luxury! I do like deep sky, and the skies around my way are fairly dark. However, I always feel that refractors excel on planetary objects, but not so on the faint fuzzies!21 November 2018 at 1:37 am #580262
Late last year I bought a 120mm F1000 mm Skywatcher OTA and matched it to an EQ5 mount and added an RA drive. (I had always wanted a big refractor.) then, lo and behold, within months the local agent was selling 150mm 1200mm Celestron OTA.s for half price. I mated this with an old superseded Celestron DX mount which I got for 43% of the price that the same mount cost four years ago for my C14.
I managed to sell the 120mm for only a modest loss.
Now, my assessment.: Chromatic aberration is a problem with achromats. The way to largely avoid it is either have a focal ratio with a CA ratio greater than 3.0 or go to an ED glass version and pay more than twice the price. The CA ratio is determined by dividing in the focal ration by the aperture in inches. Thus for a 102mm (4 inches) to reach 3.0 it would have to be F12.
Okay, so I have had a 120mm at F8.3 and own a 150mm at F8. What have I found when using them?
Colour fringes resulted, bordered by a lovely pastel yellow green shade to the limbs of bright objects like the Moon and Jupiter not to forget a violet haze on these bright objects. The purists and ‘pretty picture’ imagers, of course, decamped to purchase ED glass versions, even triplet lenses, at costs starting several times greater for the equivalent sized optical tube assembly. A further factor for the 6” or 150mm (5.9”) refractors is that with the heavy objective, the tube becomes top heavy, so there is considerably more of it is below the point of balance than above. This means an extra high mount for comfortable viewing unless you propose to observe higher objects from a sitting or lying on the floor position. In my view the mount must be high enough to allow a minimum viewing height at vertical of (say) 80cm, namely around 10cm above standard table/desk height. It must also be sturdy enough to support the ~10kg weight and any mechanical issues resulting from a longer tube.
Okay, a 150mm F8 lens (which should be at least F18 by the formula), is an extreme example. A minus violet filter will clean up the image, taking a loss of light and in my case I have a yellow filter that does much the same thing and improves contrast but gives this a dirty yellow caste. What I am saying is to use these filters on bright objects when seeking contrast and removal of spurious blue/violet, but remove the filters when observing deep sky.
For many years I have had reflectors (up to 16″), then Schmidt Cassegrains (to 14″) and have added the large 150mm refractor. My assessment of the visual tightness of the star image (admiitedly possibly unconsciously influenced by ‘seeing’) is that if reflector images are a 6, then SCT’s are an 8.5, Maksutovs a 9, and refractors 9.5. (No optics are perfect.)
Then we are looking at the weight. In Skywatcher terms, a 100mm OTA will perhaps weigh 3kg, and be okay on an EQ3, a 120mm (5kg+) will need an EQ5 (not much heavier mount), but a 150mm is around 10kg and needs much more.
I sold my 120mm to an older fellow and the whole setup probably was not more than about 15 to 16kg.
Now, though refractors look nice and classical and are wonderful conversation pieces standing in the corner of the lounge room, they are awkward and bulky, particularly to negotiate up stairs. How about a nice short SCT or Maksutov, which is much more convenient to use?21 November 2018 at 10:23 am #580263
Thanks for that Peter. I particularly found the CA value interesting and very helpful. A really good point about the use of filters re CA, but at the end of the day I feel it’s a bit of a bodge. Funny that you should mention a short tube SCT or Mak, as the chap at my nearest Telescope dealer suggested that too. However, I don’t feel a long focus refractor would be too awkward and difficult on my stairs, well not at the moment anyway. That of course could change! The other thing that really puts me off re a SCT or Mak is the relatively large central obstruction, that as you know, crucifies diffraction limited objects. Two questions I’d like to ask you though. To the best of your knowledge, do Bresser’s and Skywatchers originate from the same factory? in China obviously! Also, and I feel slightly embarrassed to have to ask you this, but can you clarify an abbreviation you use more than once, and that’s ‘OTA’. It’s obviously Off The something or other! 🙂
Like the big Newtonian behind you! 🙂21 November 2018 at 11:30 am #580264Paul LeylandParticipant
Optical Tube Assembly — the gubbins that forms the image.21 November 2018 at 5:49 pm #580265
Of course! Cheers mate 🙂21 November 2018 at 10:45 pm #580266
I will be away for a few days so any further reply from me will have to wait until after the weekend.
Regarding OTA (Optical Tube Assembly) and other acronyms, I know this can be a bloody nuisance. You are reading an article and come across one and then have to sift back through it to see the first time it was used!
Anyway concerning your question. Bresser is a distinct and different manufacturer from the people (Synta company) who make ‘Skywatcher’ and ‘Celestron’. (Bresser may be Taiwanese, but I am not sure – You could google it.) The problem comes in that brackets and fittings are probably not interchangable. You see for the 150mm Celestron, I attached a ‘Skywatcher’ mounting bar (plus rings), to mount the 80mm guide/finder. Parts are identical.
The Chinese moderately priced stuff is quite good.
Now for my SCT’s I was at first worried about the 30% plus obstruction by the secondary. Theoretically it does drop some contrast. In a practical sense for the F10 or F11 units, you would notice very little (if any difference), from a refractor. Of course out of focus images are a donut. Also, your SCT would be 127mm, 150mm or even (I would recommend) 200mm, which still weights in at around 5kg just like a 120mm refractor. At the loss of a small amount of image quality you have extra lightgrasp and resolution and more convenience in use – and no spurious colour.
Still the refractors, being traditional, have allure, and the big ones in my early days were very expensive – so I wanted one. (The dreaded ‘I wannas’.) I have one and it is nice but….22 November 2018 at 7:42 pm #580270
I agree with Peter’s comments. That graph he gives is very useful in judging what to expect with achromats. I would expect the chromatic aberration in the 127mm f9.5 to be quite intrusive, making it rather non-ideal for lunar and planetary work.
I haven’t tested these Bresser telescopes, but generally Bresser have a lower reputation than Skywatcher and Celestron – deserved or not – and much lower than Vixen (whose style they look to be imitating with their white paintwork).
I have some words to say on this subject in the December Journal, which will be out shortly!22 November 2018 at 8:11 pm #580271
Thank you Peter. I value your educated and experienced comments with interest. I shall not rule out an SCT, or preferably a Mak. You’re perfectly correct in your assumption of the allure of a big refractor, but practicality is very important. I don’t like the sound of non standard brackets either, a pity. That’s something the dealer didn’t mention!22 November 2018 at 8:21 pm #580272
Thank you David. If I did go for a refractor, it would have to be F/11 or above, because of the unwanted CA. I haven’t the funds for a multi element OG, so it would have to be the basic Fraunhofer design. Hence I would choose the Bresser 102mm F/11 model, rather than the 127mm F9.5. However, I’m beginning to get the drift that Bresser’s aren’t too good, and I do want quality, if I can afford it! Being so interested in Planetary viewing, it would be so nice to use a telescope with an unobstructive optical system. I’d go for a traditional Newt, but I have 2 old British built dinosaurs that I can’t use because of lack of any form of portability. Anyway, thank you for your input, and I look forward to your article in the next BAA journal23 November 2018 at 3:42 am #580274
Bresser is a German company that is associated with Chinese manufacturer Jinghua Optical Electronics Co. (who also now own Meade), so that probably gives where they are actually made.
One thing that’s not clear from your post, Bob, is whether you are looking to purchase a whole package: mount and telescope. If you are, we should be talking about the mount at least as much as the telescope. The mount of the Messier AR-102 looks too small for the telescope to me, judging by the picture on the tringastro site. If the telescope and mount are separate, for a manual mount, I recommend spending at least ⅓ the budget on the mount. For a GOTO mount, at least ½.
A separate 102mm f/11 OTA is sold by Altair Astro: their Starwave 102mm f/11. This looks different to the Bresser offering, and got a good review from Sky at Night magazine. I’d say a telescope of this size should not go on a smaller mount than the Skywatcher EQ5, or similar. Unfortunately, we may be getting to the point here that you would have difficulty getting this setup up and down stairs to your first floor flat, unless you disassembled it into several pieces each time.
A 150mm SCT or Maksutov would have similar image quality to a long 100mm refractor, but work with a lighter mounting, and the setup would be more stair-capable.23 November 2018 at 9:21 pm #580276
Thanks David, food for thought.
If I did go for the 102 F/11 Bresser, and it’s starting to look unlikely, then I would upgrade it and purchase the EXOS-2 EQ GOTO instead. I think one is able to do this. The smaller mount that it comes with as standard certainly doesn’t look man enough for the job.
Actually, I have looked at the Starwave, from Altair, and it does look good. I haven’t yet read the review in the SAN magazine, but I will, if it’s available on line. If I did decide to totally shy away form a large refractor, and go down a folded reflector route, then I’d try and go for a 200mm Mak, as long as it’s affordable and portable enough. Valid point about being stair friendly too.24 November 2018 at 10:12 pm #580282David GrahamParticipant
Hi Bob – I hope you don’t mind me wading into the debate. I have a number of refractors and Maksutovs which I mainly use for visual planetary observation. The central obstruction in the compound telescope does make a marginal difference in image contrast but detail revealed remains largely the same. Where the Maksutov scores is in the physical convenience of using a shorter tube. I don’t use diagonals, much preferring the ‘straight through’ approach, and certainly following a planet when well north of the celestial equator can make for some interesting times, all the more so as I’m no longer in the flush of youth! The refractor I use the most is a 120mm aperture Skywatcher achromat which with the factory focuser changed for the far superior Crayford type, gives crisp, high contrast views of the planets. One area where the refractor will score is the ‘cool down’ time is much shorter, if the instrument has to be brought from a relatively warm environment into a cool one, for use.25 November 2018 at 11:15 am #580283
I am attaching a image of the 120mm F 1000mm Skywatcher that I had for a short while. It is mounted on an EQ5 mount and aluminium tripod. I added an RA drive to it for convenient use. As I pointed out and describe, there is considerable chromatic aberration, but this is what the beast looked like. (My current 150mm setup – image above – is much, much heavier.)
For convenience of use, ease of transport, and greater lightgrasp a mid sized Maksutov or Schmidt Cassegrain is the go. The Maksutovs get much more expensive, certainly when larger than 127mm, but if you can manage it weight and size-wise, the 200mm SCTs are relatively affordable. They are quite a versatile instrument with a good amount of lightgrasp. Something of this size is still reasonably portable and large enough that any limitations are not obvious and annoying and should provide years of satisfactory use. The long focal ratio of F10 is great for lunar and planetary. The big question is the mounting where you need to limit any extra weight. For example a mount with a counterweight is ‘dead weight’ to carry up the stairs.25 November 2018 at 12:00 pm #580284Andy WilsonKeymaster
Another point to bear in mind, for the same aperture you will need a more robust mounting for a long tube telescope than for a short tube telescope. Telescope mountings are often overlooked and I agree with David’s comments. A good mounting makes a huge difference to usability and enjoyment of a telescope.
I am not trying to put you off a refractor, as a good refractor is a joy to use. However, the long distance from the eyepiece to the mount will multiply up any small movements in the mount and tripod.
Andy25 November 2018 at 6:57 pm #580285
Thank you Peter, David and Andy. All of your points and facts you’ve raised have been more than helpful, and have really made me think on what I really need, and what I don’t!
I am shying away now from a big refractor, soley because of portability. As I’ve already mentioned I think, I have two big old heavy dinosaurs sitting (in pieces) in my cupboard, that I’m unable to use because of lack of portability. For the record, one is a Charles Frank 6″ F/9 reflector, and the other, an 8.5″ F6 Newtonian, built by AE. So I don’t need to shell out a great deal of money to add a yet another telescope to the cupboard! You’ve all recommended a folded reflector, and with this in mind, I am now hankering towards a good sized Cassegrain, but not a closed tube design, mainly because of dewing on the corrector, and large central obstruction. If funds permit, I’d really like to avail myself of the Takahashi Mewlon 210. It’s a Dall Kirkham design, and the quality is second to none in my mind. I think it will still be portable, but will be on the limit, I understand that, but I want the mount to be substantial. Does anybody have any experience of the Mewlons? I once had the use of a fine Takahashi refractor, over 30 years ago, and I was truly amazed at the quality. I might have to go 2nd hand though 🙂 as I know that we’re talking megabucks!26 November 2018 at 7:47 pm #580286
Yes. The idea of carrying an f/11 4-inch refractor on an adequate German equatorial mount up and down stairs doesn’t seem like a realistic option to me.
I don’t recall ever looking through a Mewlon, but everybody says they are superb. However, there are advantages to the closed-tube cats, and I don’t think you should dismiss them out of hand. They stay clean inside, they don’t have spiders (either the animal or the optical kind) to affect the image, and the coatings do not corrode rapidly (this latter factor I find to be a huge issue in a polluted city for open-tube scopes). Dewing of the corrector is an issue, but can be greatly slowed with a dew shield, which can be a flexible piece of plastic. The ‘large central obstruction’ is a bit of an over-done preoccupation of some people, in my view. The great telescopes of the world (and in space) all have obstructions of 30-40% of the diameter, and no astronomer ever thought that made them bad telescopes. Contrast comes from many factors, including cleanness of the optics and darkness of the tube (baffling). SCTs tend to score well on these. The central obstruction throws a bit more light into the first diffraction ring, and if observing close double stars in fantastic seeing it is an effect you might possibly detect, but it doesn’t seem to damage planetary detail. I’ve been happy enough with Celestron SCTs to have owned 5 different ones.
My other thought on all this is that, to save weight to be carrying, you could consider: do you really need a German equatorial? As Peter says, they imply that annoying counterweight. There’s an increasing selection of altazimuth mounts, manual and driven, available now. Most of them, again, I haven’t tested, so how well they might do in your context I don’t know. But another correspondent of mine is currently having a lot of fun with a Skywatcher GTi altazimuth GOTO (but only with a 75mm short-tube refractor).
As far as the 2nd hand market goes, I’d recommend UK Astronomy Buy & Sell for bargains. I’ve bought loads of things off there over the years, and rarely had any problems.27 November 2018 at 7:45 pm #580291
Thank you for even more worthwhile comments and input David. Good point re an altazimuth mounts, and being a bit old school, it is something I haven’t really thought of or considered. Having said that, I am so used to using German equatorial’s that I think I’ll be all at sea with them. Besides, I love the simplicity of an equatorial mount. I will give it thought though. Good point about the central obstruction issue, and maybe many do make too much of it. However, when one purchases or constructs most things in life, it generally involves some form of compromise, and I see an over large obstruction as just that, especially when it’s diffraction limited objects that one is observing. My eyesight isn’t the best and I always feel I need all the help I can get! Although I’m old to this game, these days I don’t get much chance to look and test the latest equipment, so I do realise I might be a little out of touch with things. I just seem to have memories of everybody purchasing Meade SCT’s and suffering huge dewing problems, as well as large amounts of image shift due to poor construction of the focusing primary. If I can’t go as far as a Mewlon, then a Vixen might be a good alternative. I’m not being a snob, but I don’t have too much faith in stuff from China, though I know it’s usually where the sourced labour is cheapest and exchange rates and so on and so on. Before I part with large sums of money, it would be a good idea to star test a few ‘copes. Getting the opportunity to do this could be problematic though.
I will check out UK Astronomy Buy & Sell, always preferable to anything like Ebay or Gumtree!4 March 2019 at 5:06 pm #580796
I’m back on the hunt for a decent telescope setup. Having read through all the very helpful replies, particularly from Peter and David, I am still considering a refractor, but ditching the idea of a Bresser, mainly because of unknown quality. However, although it’s much more costly, I think the latest Starwave Ascent 102 ED/F11 on a Skywatcher HEQ 5 mount might be a worthwhile combination? The previous Starwave 102/F11, non ED (and much less expensive) is now sadly discontinued, but reviews of this one are good. So, does anybody have any experience of the ED version, is it worth the extra dosh, or would It be better to seek out a 2nd hand earlier non ED version? Also, is the HEQ5 mount overkill, and would a EQ 5 be adequate? I realise that one can never spend too much on a good mount, but I don’t need to go silly with the hard earned funds. Also, there are still my stairs to consider, as mentioned previously, so that has to be taken into consideration.
Sorry to bend everybody’s ears on this one again, but I really don’t want to get something that is rubbish. I have banished the thoughts of Vixen and Takahashi…..over the top for me!
- You must be logged in to reply to this topic.