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First time ED / APO buyer for AP


Peter_D
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Hi

I'm looking at buying my first imaging ED or APO refractor in the new year (or a bit later if I need to save!).

Background: I have several other scopes for visual / planetary so it'll be for DSO imaging only. I have a Vixen GP (so EQ5 equivalent) with the Skywatcher GoTo upgrade kit installed. This will be my AP mount for the first year.  I would like to get a portable mount as well but this is down the line.

Budget: Up to £600 (700€). I understand that a corrector is a prerequisite but this is something I would buy later, getting the right scope is the priority.

I have an un-modded Canon 60D DSLR.
I live in a Bottle 6 area. 

Any advice on the  glass, focal length, aperture I should be aiming for that will fit my experience level and mount?  Many thanks for any suggestions. 

Clear skies

Peter

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I think you might need to do some more thinking before you buy. I’m not familiar with the Vixen GP or the Sky Watcher upgrade but do you know that it will be suitable for AP? I.e. is the tracking accuracy (periodic error) acceptable.
 

You also mention a more portable mount in the future. I presume the plan is to use it with whatever scope you end up purchasing. Can you define more portable? You need to think in terms of realistic payload for AP because that will determine what scope is best. 
 

Next do you have an idea of what targets you would like to shoot? You can see what FOV you would get with various scopes and your 60D at astronomytools.net. Then you can narrow it down even further. 
 

Then you have to consider whether you need guiding. The higher you go in focal length and the less accurate  the mount means a higher likelihood you will need guiding. 
 

With all that considered I would imagine you’re going to be in the 300-500mm FL category where one of the ED80’s mentioned above would be a popular choice. There are a number of choices in the 60-70mm aperture range too. SkyWatcher ED72 where you’ll fit the reducer in on your budget too. SharpStar 61EDPH or William optics are others. If you can stretch the budget another £99 then the WO Redcat 51 could be a good choice too. 
 

As you can see there are a lot of options. I think what you want to image and the final mount situation will have more of a bearing on your choice to be honest.

Edited by Icesheet
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Thanks @Icesheet, great post! Lots of food for thought.

Yes, I understand the mount is key in AP. That said, I just can't justify the expense on a new mount at the moment - better I think to see what the results are with the GP and go from there.  

JUSt a quick follow up question - is the jump that noticeable from 60 to 72 or 72 to 80mm in AP? I know aperture is king in visual but in AP, I guess we are looking more at glass type, lens quality and build of scope? 

Edited by Peter_D
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Aperture is not so important in AP because the camera can collect light over time, which the eye cannot do. A quick list of priorities would be:

- Choosing a focal length at which you want to image. See what your camera's APS-c chip will frame at different focal lengths.  If you have any doubts about your mount it would be best to keep the focal length short so that less tracking accuracy is needed.

- Colour correction, particularly at the short wavelength (blue) end.

- Focuser quality.  It needs to be a properly on-axis, tilt-free focuser which will hold the camera's weight.

- Image circle must be large enough for your chip unless you are willing to crop.

 

In your situation I would think about the mount first and whether or not it will autoguide well. Until you have an accurate, well guided mount you are, to be brutally honest, rather wasting your time.

Olly

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32 minutes ago, StarryEyed said:

Olly is right. Mount first. 

The trick is to work well within the limits of the mount then you will enjoy yourself. 

Have you tried guiding with an existing scope to see how good your mount is and piggy backing the dslr. 

 

I had set up my C6, an OAG and my planetary cam just to get PHD2 working. It kept losing the guide star so I figured it might be a better strategy to use a lighter OTA and guide camera, hence my post.

I do have a Mak90. Maybe then a good idea to set this up guiding on my GP and get back to you with the guiding results?  What would be deemed acceptable results in RA and Dec?

Edited by Peter_D
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Get it guiding as no matter what scope you mount on it you still wont know why you cant guide with it.

Get to know your mount and work out its limits then lower the bar,  dont try and do more than its capable of. 

A misbehaving mount can wipe a smile of your face for a week.

Enjoy your hobby. 

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7 hours ago, Peter_D said:

JUSt a quick follow up question - is the jump that noticeable from 60 to 72 or 72 to 80mm in AP? I know aperture is king in visual but in AP, I guess we are looking more at glass type, lens quality and build of scope? 

Olly covered this. Aperture shouldn’t factor greatly in your decision. 
 

I wouldn’t try guiding with a C6 or a Mak 90 tbh. Can you use one of your camera lenses? If you can connect the 60D to your laptop you could try with that. Otherwise, try and see what you can get unguided with the camera and a lens. That will also give you an idea. 

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icesheet makes a good point about the c90.

You can try bining the camera 2x2 and defocus the for a bigger star image and take longer exposures. Just remember your experimenting and see what works. Keep notes of what you changed and the results you got. Collect guiding to tie in with your notes. 

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WO Z61.

Compact - check

Within budget - check

Additional - Widefield, DSO, lunar, solar (with appropriate filters), planetary (to a degree), excellent focuser, optics - multiple check

Edited by Elp
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  • 1 month later...

Update: A used Evostar ED80 came up for sale and I was successful in my bid for it. I bought a svBony 30mm guidescope and got PHD2 working using the ST4 On Camera method (for now). I was out yesterday and captured an hour's worth of data on the Pleiades. Lot's of room for improvement but definitely a easier scope to use for AP with my GP mount than my previous  attempts with a C6.

IMG_20220108_181535056_compress99~3.jpg

m45_2_16B_Finished~7.jpg

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Oh, bravo! You're on your way now.

One caveat: If the guidescope is mounted atop that big "stalk" designed for a finder scope, you may encounter issues with differential flexure. Since guiding involves detecting and correcting deviations of a fraction of an arcsecond, absolute rigidity is a big advantage. Mechanical slop which you can hardly even feel can translate to multiple arcseconds' worth of flex. The classic signature of that problem is for the guiding graph to be showing nice smooth low-error lines, and the stars in the imaging scope to be streaked, egg-shaped, or just extra-large.

No sense in chasing the problem unless you see it happening, though! The stars in your Pleiades image look reasonably round to me, at least in the center (the corners do show some issues, which is probably not guiding).

That is a great start!

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Congratulations Peter. I’ve been following this thread closely as I’m in the same boat you found yourself in. I already have two scopes and now want to have a go at AP. I took on board the mount being stressed over and over again, therefore I’m getting ready to buy myself a HEQ5 pro. I can then look at the scope to buy. Good luck in your endeavors Peter 👍

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Thanks! The photo is a bit misleading because I took it just with a normal  finder scope attached. The SvBony guidescope is much lower and worked a treat. I just had to unscrew the lens element out to achieve focus as my Zwo asi224mc screws directly into the back threads of the guidescope.

I still have to get a corrector so that should help with the coma around the edges. 

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