Wide field scope or different camera

[nexusjeep]

Right here goes,

For a while I have been pondering a wider field of view to get some larger objects or more of very large objects in shot. So have been looking at the potential of a small wide field scope something like the hope D60 from Touptek. I am not planning on being mobile with it so it would be on the existing setup so there would be a cost to mount plus the faffing around to get everything to fit.

however, I am now thinking the other possibility would be to go to a full frame camera there are several reasons to this thinking one is I have a very expensive refractor already with the APM LZOS 780/130 + 0.75x reducer and Esatto 4" focuser so have a big image circle available.

The image below is the field of view I currently have with the ASI2600MC camera and the 0.75x reducer on this scope, the ASI6200MC gives me something in between the Hope D60 using the current ASI2600MC. The big plus to the full frame camera on the existing setup is that I would still be sampling a 1.36 arc seconds per pixel were as with the wide filed scope and the ASI2600MC I would be at 3.89 arc seconds per pixel.

Anyone have any thoughts on this, note the comparison image has a 0.73x reducer not a 0.75x as for some reason that was not an option on the tool.

astronomy_tools_fov.png (191.18 KiB) Viewed 719 times

Cheers
Nick

[turfpit]

Nick

Run your figures through the CCD Suitability calculator, I think the sampling will answer your question.

Dave

[nexusjeep]

Hi Dave
I did that and my original scope at 1x is 1 pixel to 1 arc second and at the 0.75x reduced length 1 pixel is 1.33 arc seconds so well within the 0.67 to 2 arc seconds recommendations for 2-4" FWHM Seeing. The Hope D60 Touptek scope it states the pixel arc second value of 2.77 and then says under sampled but then says ok for wide field imaging but a friend has the Askar SQA55 his image look okay but they are noticeably less crisp/ defined than when he images with his larger Williams optics scope on the same ASI2600MC Camera and I see the same when comparing detail on my images to his SQA55.

So this less crispness/ defined scenario was why I was after opinions and is why I think I am leaning towards the larger full frame camera as it gives me about an extra third ish coverage of the sky but is a lot more in the sweet spot for the pixel arc second rule even when seeing is better than 2 - 4" FWHM and the objective on my scope will never be seeing limited.

Just need to work out which body part I can afford to sell next

Cheers
Nick

[admin]

Hi,

I would just add that side-by-side mounting of multiple scopes is great from the point of view of having different tools available to you with no need to swap equipment, but a pain for a number of other reasons (I have 3 side-by-side)

* You have to balance in 3 directions now, since the RA axis can be balanced when in the home position but unbalanced at 90 rotation (or vice versa)
* This needs re-checking every time you tinker with equipment or change cameras or similar
* You need to get the fronts of the telescopes roughly lined up (especially for anything short focal length) as otherwise one telescope sitting forward of the other can actually cut into the light collection of the scope further back, giving you problems that look like they will be cured by flats but actually aren't

As such, the bigger camera may be simpler. But, just to add confusion, aren't there two different full frame options, one with smaller pixels and one with larger?

cheers,

Robin

[turfpit]

Nick

At nearly £4k, how much of your body can you do without? What a money pit of a hobby this is.

Getting the sampling right is always worth going for. Having 2 scopes and the equipment changes is going to be harder. You could possible end up having the 6200 in a permanent setup and sell off the 2600.

A couple of things to consider for wider fields:

• mosaics

• 135mm lens, see https://www.astrobin.com/rdov6c/

Don't forget to budget for disk space when you discover what the 62 in 6200 means.

Dave

[nexusjeep]

Hi Dave / Robin,
My guide scope is a Skywatcher ED72Pro with a 0.8x reducer so currently investigating sticking the ASI2600MC in that to see the field of view and guiding off of the 130/780 LZOS so the guiding may be a little overkill . Dave disk space is not an issue as the observatory PC has a 4tb SSD in it and the observatory is on 1 gig ethernet into the house network and dumps to the server in the upstairs utility room and that has a 24tb raid array in so plenty of space.

Holding fire for a few weeks on making a decision as my other hobby is rallying on the full motion rig I have and there is a new Rally sim coming out that may force me to upgrade to a RTX5090 so may be temporarily diverting funds to that as I can use that when its cloudy/raining hence investigating using the ED72 which is 420 focal native and 336 with the 0.8x reducer.

Cheers
Nick