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Posted by Tom Moran at 11:29 on 2010 Oct 17
Hello.I am interested in following the giant planet. I have a 120mm achromat at f8 and use a web cam to image with. I am considering upgrading to get better images in a year or so. How much improvement would I see in a 152mm achromat? I enclose an image taken on 16 Oct for reference. I would like to eventually contribute to Jupiter section and I am looking for a telescope that can do this and will not break the bank!Regards.Tom MoranPS: Have I got the satellites correct? North up and east to the right.I find if i image in B/W I can minimise chromatic abberation. Would a minus V or equivalent filter help with this?
Posted by Tom Moran at 13:08 on 2010 Oct 17
Hello.I don’t know if this will work, but here is a link to my JUpiter image:http://www.flickr.com/photos/48778860@N06/5089337618/RegardsTom
Posted by David Mottershead at 19:34 on 2010 Oct 17
HelloWhen using my 120mm refractor (see here, http://britastro.org/baa/index.php?option=com_kunena&Itemid=100007&func=view&catid=18&id=195#201), and depending on what I am viewing and the magnification I am using, I stack Baader Neodymium and Fringe Killer filters, giving the same results as the Baader Semi APO filter. The advantage of having the two (I already had a Neodymium filter, so simply added the Fringe Killer) is that I can still use them individually, e.g. the Neodymium to reduce light pollution etc, but then gain the benefits of the equivalent of the Semi APO filter when stacked – and the Semi APO is apparently well regarded as a planetary filter when used in achromatic refractors.As for the 150 refractor, that will give more light grasp than the 120, allowing finer detail to be seen, and will allow a higher theoretical magnification, but in reality I’d suggest that the highest magnification that you might use on the 150 will be pretty well the same as that of the 120 – and magnification isn’t what it’s about anyway. The better light grasp on the other hand is always worth while to catch the finer, more subtle detail that a smaller scope can’t resolve. If your main interest and area of observation is lunar and planetary, have you considered a Maksutov? These are, in my opinion, one the best lunar/planetary scopes around.A good image of Jupiter as well, and nothing wrong with black and white.Hope this is of some use.
Posted by Tom Moran at 08:18 on 2010 Oct 18
David.Thanks for that. The fringe killer is certainly on my list. I have the Orion Skyglow. Would I get the same result stacking it with the Fringe Killer? I had discussed my telescope upgrade with Andrea Tiselli and he thought highly of the Maks also. I think it is down to a 10 inch Newtonian or a 180 Skymax Makustov. I enjoyed your web site.Clear skies.Tom
Posted by Andrea Tasselli at 00:18 on 2010 Oct 19
Hi Tom,Refractor unless they are large (over 6") and for achromats long (very very long; for a 6" at least f/15 to f/20 really) are not worth considering for imaging purpose. These filters are , in my humble opinion, just hiding the issue by removing or diminishing some of the offenders. Ditto for b&w whereas you can’t see it but it is there anyway. The only safe way to image using achros is to use a monochromatic imager and RGB composite technique to get rid of CA (but you’d still get chromatic spherical aberration the faster the telescope the worse it is going to be). Reg’sAndrea T.
Posted by Tom Moran at 12:54 on 2010 Oct 19
Andrea.I know you are absolutely right. I just like refractors and a large APO is out of my budget. Following on from our conversation in the Telescopes section it will either be a SkyMax Maksutov 180 or a 10" Newtonian upgrade in a year or so.Regards.Tom
Posted by Nick Atkinson at 18:00 on 2010 Oct 30
There are several variables to consider a larger telescope will look through a wider column of air. With good seeing a 12" scope will always be able to see finer detail Using my 150 triplet I have failed to see the red spot despite using different coloured filters. I always remember looking through the army telescope at Aldershot I believe a 10" F15 achromat and the colour of the red spot was quite brilliant but then I was 18 not over 60 as now. So perhaps another thing
to consider is how good are our own detectors in both eyes. My right eye is much better than the leftAnother factor over which we have some control is the eyepiece so everybody which eyepiece is best for planetary work? Posted by Andrea Tasselli at 09:39 on 2010 Oct 31
Hard to say. Usually the best advice is to try before you buy as something that work fine for one individual might not going to work that well for some else. You also need to account for astigmatism if you have any. As a rough guide I would say that Vixen’s ortho are quite OK but Zeiss own old ortho (.925" barrel) are very very good. Also very good are Pentax’s SMC ortho line (again .925" barrel) and Takahashi LE series. Of newer design I’d reckon that TV Radian series is quite good as well the TMB SuperMonos. One key thing to look for is for good AR coatings in an EP, probably more than the specific of the design itself. Besides that simpler designs with narrow AFOV are probably better suited than very complex wide-field designs which usually compromise on on-axis correction to achieve better field correction.Andrea T.
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