There's no need for that, yes I did read the posts. I was just trying to infer that unless the same person takes the photos with the same imaging gear from the same location, it wouldn't really give you an accurate compare between the scopes.
Ie suburbia, cheap camera and an apo won't compare favourably to a good dark sky location and good camera with an achro.
From a scientific standpoint, to give you the most accurate info and answer your first question, ideally, the same person will have all the gear and take the photos back to back with all other variables the same.
cjamo9, i think that site is just to give you an idea framing, ie with a certain scope/camera combo how the image will frame, or in other words how big the object will show in your photo.
We might get lucky yet, there are a lot of guys out there with a lot of different gear and might be able to do all of it. Cross your fingers!
I'm curious too, also about the difference between a top quality achro vs a lower end apo. I wonder if it is as cut and dry as 'apos are better' and that's it? I suspect not.
Confess I'm interested as well. The $$ difference is substantial APO vs ACHRO and I'm impressed with what I've seen posted with just 80mm APO scopes. I have an 80mm Achro and I am quite impressed with just how well it does work but I suspect photographically the faults will appear.
I am going to try some solar pix hopefully soon through Baader film. Being almost monochromatic, colour abberation should not be an issue and will let me see how good the scope is in that role.
I'd like an APO but ... we'll see.
Silv, know you are not interested in solar system imaging, but others seem to be and you invited input from that area. will remove post if you think it too far from the thread theme.
Achros are pretty much as good as APOs if you restrict the waveband and many solar system objects can be imaged OK in monochrome. The attached images are all with bottom end achros and a QHY5 colour cam - a fun combo. Standard Registax stacking was used for all images.
Venus transit through Celestron 80mm f11? achro - Celestron solar filter + green filter. 4 panels stacked and much detail lost fitting it into posting limits (its actually 4x this area)
moon and Venus through super low cost Meade 90mm f8.8 achro (and 2x Meade Barlow from fading memory). Images assembled from green data only.
Shiraz, you have a livelong permit jumping into any of my threads!
Of course, I'm happy to extend the subject to solar system, incl moon and sun.
Peter I think already made the point about planetary interests.
All for the greater good.
As long as the images are not an editing contest and as long as the imaging path is well described, no fancy device being used is preferred. (And I have no idea what "assembly from green data" refers to. That's running under "fancy" in my book. )
(And as long as someone gives me light frames of NGC 3372. )
I'm really happy that the comparison is of interest to others, too.
ZeroID: I have an 80mm Achro and I am quite impressed with just how well it does work but I suspect photographically the faults will appear.
you can't mount your camera to it, can you? that's a pity.
although - it would probably take you half a year to come up with example images, given the weather we suffer from here in Auckland.
(And I have no idea what "assembly from green data" refers to. That's running under "fancy" in my book. )
naah nothing fancy at all - when converting colour images to B&W, most software allows you to specify how much each colour contributes to the luminance - need to set red and blue to zero to remove colour fringing from the achro image.
just to be sure - are you asking for comparison images of NGC3372? - I think that is what your image shows.
I think you just need a well focussed raw photos of the bright open cluster, for example Hyades, so that you can see the star image difference in centre and in the frame corners.
This will give you all the information you need, applicable to planets, stars, nebulae... You will be able to determine and compare the amount of coma, CA, astigmatism, field curvature for each optical system.
Yes, there is a lot of water muddying when comparisons between various optical systems are concerned - sometimes people feel they have to protect their investments (mostly from themselves). It is bad feeling you paid k$ for something that doesn't perform ..
Of course, general rule definitely applies here - "You get more music for more money..."
[...open cluster...] This will give you all the information you need, applicable to planets, stars, nebulae...
That's a grand idea. Do you have single frames of short-ish exposure of it, captured through a newish achro or apo or both?
Might well be very useful!! Thank you!
However, I'm a noob. I can't tell anything from seeing an open cluster. My sole "experience" is a colored nebula - NGC3372, as I now know. I've captured/seen it with a 200mm lens and with my 8".
Well, and Orion - but only with the lens in pre-telescope times.
Now, I need to do something with my setup - which means spend money.
So, I'd like to see the difference in colorful big objects of achro and apo, 80mm and bigger. Maybe I can live with what I would get through an achro? That's what I want to try and find out.
And other noobs might be interested in planets and the moon and the sun and would appreciate a comparison in these objects before they spend all their money on an APO
Annette ,
The thing with open cluster is, it consists of stars, more or less randomly distributed.
Stars are point-like sources of white (more or less) light - and ideal optical system will produce images of stars which are point-like, across all the frame.
The real systems, however, will produce images which will be distorted - that means, those images will not be points, and each wavelength from their spectra will produce it's own image more or less at the same place on the frame.
So, it will be immediately visible which optical system produces closer to ideal star images.
Anything else (any other target - nebulae, or planets or Moon) will not be able to show you that, simply because those light sources are not point-like.
so people interested in pointlike stars will want to see examples.
I'm still interested in whether I can live with the outcome of colorful nebula, or not. I'm not in it for the "art of perfect imaging". I want to discover. That's all.
Let's open the imaging subjects completely, shall we?
Maybe I can live with what I would get through an achro?
Then go straight to achromatic lens - you will live just nicely .
If not, you can always reduce the aperture for one stop (and take 2x longer exposures) this will do the trick for you.
Mostly unedited,
single frames
of short-ish exposures
taken through new-ish achro
and apo refractors
of 80mm +
with little to nothing else in the imaging path.
I posted these images in my ED80 thread but I'll put em up here again.
The Jewel box and Mimosa in Crux comparison. Pic4 is from a 71mm achromat and pic5 is from an Ekinox ED80. As Bojan mentioned, achromatic scopes can't focus all colours at the same focal plane. You can focus red, green and blue individually but not all at the same time when shooting one shot colour. What happens is one or more of the colours will be out of focus in the achromat and bloat, giving a red, blue or violet fringe.
On the other hand ED or APO scopes do a better job at focussing all the colours at the same focal plane.
I've included a close up of halos caused by the red plane out of focus using a 4 inch achromat.
we'll see.
)
