celestron edge 8 hd for dso

[iwols]

would the above scope be any good for dso with a nikon dslr as this has a good fov for my needs cheers for any comments

[souls33k3r]

Because i own one and i know the issues i would say "No". The back focus will be the main problem. Allow me to explain, imaging at native f/10 is going to be impossible, you will need to introduce a focal reducer which will being the scope down to f/7 (1422mm), when you introduce the reducer, you have already eaten up the back focus.

EdgeHD 8 total back focus is 133.5, when you bring in the reducer it will bring it down to 105mm.

Now the Nikon DSLR will have a back focus of 55mm, you will need an OAG to guide of course for longer exposures (longer than 2 min) which will eat up another 29mm and the DSLR T-ring will eat another 48mm.

So DSLR 55mm + OAG 29mm + DSLR T-Ring 48mm = 132mm which is way more than 105mm so impossible.

I would suggest, go with a refractor. Don't make the same mistake i made.

Hope this helps

[iwols]

thanks its just that i have the edge but been using my ed80 for the cigar galaxy/bodes,but the image is far too small ,i know i can crop but would like a bigger image to work with see single image

BODES_LIGHT_50s_800iso_20160714-00h54m21s601ms.NEF

Edited July 14, 2016 by iwols

[souls33k3r]

If you like some help with the FOV, try this link. I hope this helps. But trust me, imaging without the reducer or an OAG is going to be like pulling teeth ... EdgeHD 8 is a fantastic scope, don't get me wrong but at it's native focal length its best suited for planetary imaging. For DSO or faint objects, you will need a tracking mount, a reducer, an OAG which will then lead you in to CCD area, you'll then need a guider, filters ... it's a money pit lol 

http://astronomy.tools/calculators/field_of_view/

[iwols]

thanks already have an heq5 goto, filters  filter wheel ect(not used them yet) and qhy5 mono(only used on planetary),the link is where i thought the edge and my d750 would be a good size,maybe its my dsl thats the problem for fov

[Uranium235]

If you already have the Edge, and a mount capable of supporting it - then your next step is a CCD. You wont be doing big targets with it, but you can concentrate on the smaller galaxies or PN's.

[kendg]

First off, will the mount you have be sufficient for the camera and the OTA. Normal rule of thumb is the camera and OTA should be at 50% of the capacity of the mount.

Secondly, give it a whirl and see what happens. To control the Nikon you can try Backyard Nikon.

Third, once bitten by the AP bug, prepare to have and empty wallet, a lot of frustration and tons of fun and learning. 

[iwols]

48 minutes ago, Uranium235 said:

If you already have the Edge, and a mount capable of supporting it - then your next step is a CCD. You wont be doing big targets with it, but you can concentrate on the smaller galaxies or PN's.

next problem is what camera to go for instead of my d750??

[Feral Rabbit]

There are easier OTA's but if you have an Edge already it's not impossible (depending what you want to photograph of course).

This guy uses a Canon DSLR but I am assuming yours will be similar

Linky  One of 4 videos in the series from set up to processing

 

Hope this helps

 

Regards

[Uranium235]

4 hours ago, iwols said:

next problem is what camera to go for instead of my d750??

Now thats the milliion dollar question!

It depends on how much you can afford, and what pixel size and resolution you want to work with. Also, you will need a guidescope that is up to the task - possibly an ST80 or a barlowed finderguider.

[Ken82]

The back focus of the edgehd optics is 146mm. There is a special t adapter which will give you the perfect spacing with or without the focal reducer . 

I use 11"edge -focal reducer-t adapter -t ring- dslr. Perfect although you'll need a serious mount for this sort of focal length 

[DaveS]

The BF of the 11" Edge HD with reducer is different.

You may get away with a very slim OAG and a filter drawer. I think they are 19mm and 15mm respectively from TS.

I also have a horrible feeling that even an 8" Edge HD on an HEQ5 might be pushing it a bit.

 

Edit: Here's the FLO page for the 8" reducer https://www.firstlightoptics.com/edge-hd-series/celestron-reducer-lens-7x-edgehd-800.html It specifically says DSLRs are problematic with that particular 'scope / reducer combination.

Edited July 14, 2016 by DaveS

[iwols]

Thanks should say its the heq5 pro

 

 

 

[Ken82]

I do agree, with that sort of weight and focal length I'd say the heq5 would struggle ! 

You would need guiding accuracy of under 1 RMS to get a nice star shape. 

 

Thanks for the info Dave  I wasn't aware the 8"edge was different . That's odd as these scopes were specifically designed with aps-c sensors in mind yet the 8" is problematic and the 9" doesn't have a fr! 

[ollypenrice]

You cannot ignore the pixel scale when thining about an imaging rig. If your pixel scale is too small for your local seeing and your guiding to support then your long focal length is simply not going to bring in more detail. You will reduce the FOV without increasing the resolution, which is clearly a waste of time. (You might just as well resample a shorter FL image upwards in software.)

It might also be worth remembering that, within the backfocus of an SCT, you really need room for an off axis guider. Using a separate guidescope with an SCT is not a good idea.

Accurate guiding is not just about round stars. Random errors produce round stars but resolution is still lost.

Olly

[ianmacd]

Sorry for asking what maybe a dumb question, but can't the edge take the camera in place of the secondary mirror to give you a much lower focal length? Wouldn't that be better for DSO's?

[Waldemar]

23 hours ago, ianmacd said:

Sorry for asking what maybe a dumb question, but can't the edge take the camera in place of the secondary mirror to give you a much lower focal length? Wouldn't that be better for DSO's?

There are no dumb questions, just dumb answers...

Yes,  a HyperStar from Starizona is needed for that. The optimized imaging circle will be about 25 mm, hardly big enough for APS-c. It is not easy to get a HyperStar working well... needs quite a bit of very precise collimating.
The very steep lightcone of the HyperStar set-up presents a new set of problems...The total package: f10 original ; f 7 with the reducer and ± f2 with the HyperStar is very appealing... and quite all round, I think. Not suited for full frame, though.

Waldemar

[ollypenrice]

Hyperstar. The numbers look great. The pictures are not always that good...

 

Edited July 28, 2016 by ollypenrice

[Geordie mc]

If you have the Edge already, the t adapter and a t ring are cheap and worth a try. The manual with my Edge says use the full t adapter 105mm for DSLR's and only use half of it with the reducer which needs 93mm. Must admit I use a refractor for DSO's and the Edge for solar system work. The long focal length would mean even a vey well polar aligned mount would struggle to track accurately for anything more than 30 seconds, but brighter objects might be okay. A CCD with OAG would be much better.

Edited July 29, 2016 by Geordie mc
Pressed submit before I'd finished post

[Johanvk]

I'm since a few months experimenting with an Hyperstar on (an orange) C14 with a Losmandy mount. So far it looks promising. The reason to go for an F2 system is that we already have good greater F-ratio telescopes on site. Also an OAG was almost impossible to use, because finding suitable guiding stars was a (wasteful) time consuming, and frustrating, job. A more expensive guider camera was not in the budget.

The speed is indeed amazing, which is important considering the small amount of clear nights here. Autoguiding is done with a guiderscope, but I want to see if that is really needed at all, with such a short focal length, and such short exposure times of subs. The chip of a DSLR can be covered rather well (using flats etc.). The reported problems with the very small focussing range were not encountered - just turn the knob. A limitation is posed by the pixel size of 1.3". I'm not sure what the effect of tha limitation is on the sort of photometry I want do do. So far I did not test (narrow band) imaging through filters. On any bigger telescope these become exponentially more expensive... Testing is still going on.

For a (more modern) Edge I would certainly consider an Hyperstar, especially because the F2-F10 set-up can be switched so easy.

[UKAstroBill]

The back focus calculations change somewhat if you work with a Nikon Z system with a much smaller distance to the sensor in the camera. I think it makes the Edge 8 a much more practical proposition.