CCD Camera focusing/fov on SCT

[DoubleScoops]

Hi all, first post on the forum.

I'm just getting into Astronomy after many years of being interested in the idea, and am just getting to grips with the Celestron Evo 9.25 and all the extras I have annoyed the wife by buying.

The one aspect I am confused about is how my Skyris 236 CCD will work when attached to the visual back of the scope. After playing around for a bit it seems that what the camera sees is not quite what I expected, I guess many here will think this is a very straight forward topic but I have searched high and low for a more detailed explanations and cannot find one. I'd really appreciate any information/advice that forum members have on the following;

Firstly after focusing an object through an eyepiece and then attaching the CCD there is a great deal of focusing required to get the image re-focused. This creates an issue as I have a JMI motofocuser fitted and it takes a long time to get there, in fact a few times I have removed the JMI and then carried out the majority of the refocusing by hand! Can someone provide any information on how far the two focus points (for eyepiece and CCD) could be apart? It seems the two are on opposite ends of the focusing scale. I guess when I get more proficient with the CCD (I'm very interested in the photographic side of astronomy), the focusing between the two will not be required as often.  

Secondly, and this may not be easy to answer, if I have a Skyris 236 CCD attached what percentage of the available FOV, compared to say a 40mm eyepiece, will be visible? Will the view be comparable to a specific eyepiece focal length?

I'm enjoying the discovery process of getting used to the Evo, understanding what can be expected from the CCD will greatly help in this.

Thanks for any input you may have.

 

 

 

 

 

 

 

[Filroden]

Here’s your FoV with M1 as the background to give you an idea of scale.

http://astronomy.tools/calculators/field_of_view/?fov[]=93||118||1|1|0&messier=1

and Jupiter

http://astronomy.tools/calculators/field_of_view/?fov[]=93||118||1|1|0&solar_system=jupiter

You've got a great scope for visual and for imaging the moon and planets but it wouldn’t work well for deep sky objects for a range of reasons, manly being able to track the object for suffice to time to get a decent exposure.

[DoubleScoops]

Thanks for linking that web site, very useful.

When I bought the Evo I was aware of the discussion about how good it would be for astrophotography of DSOs, etc. but it ticked many of my boxes. I have the HD Pro wedge and am having reasonable results on getting it polar aligned, with the help and hindrance of Starsense. I also have a guide scope and am playing around with PHD2, again with reasonable initial results. For me the challenge of getting it all working together is part of the enjoyment.

[Filroden]

It’s definitely possible but it’s a lot more work than other set ups  I didn’t have the wedge and I used a much bigger chipped camera so had a bigger field of view but did manage some acceptable (to me) images from the Evo. StarSense made goto so much easier. One of the hardest parts was just getting the target into the field of view.

[DoubleScoops]

47 minutes ago, Filroden said:

It’s definitely possible but it’s a lot more work than other set ups  I didn’t have the wedge and I used a much bigger chipped camera so had a bigger field of view but did manage some acceptable (to me) images from the Evo. StarSense made goto so much easier. One of the hardest parts was just getting the target into the field of view.

Speaking from a theoretical position, the wedge is an absolute necessity for the photography. The backlash in previous mounts has been greatly reduced with the new worm gear, and the tripod is much more stable than previous offerings. The polar alignment bug in the Starsense software has been a problem but it looks like that has been solved. With good alignment and optical guiding I am hopeful that the Evo 9.25 can be a reasonable astrophotography platform...although I am ever the optimist!

[2STAR]

The Alt/Az mount of the evo 9.25 works very well with the Atik Infinity Mono or OSC, it will track easily for 120 secs with no star trails & decent images can be had,although not as good as with using a dlsr & eq mount. so maybe your camera is not the best suited for an Alt/Az mount.( unless you fit a wedge)

The main issue with the Evo is the Nexstar HC obtaining good initial alignment and you will find it is a very debated issue on what procedure works and what  does not, there are many many articles on SGL & CN so good luck.

[DoubleScoops]

10 hours ago, 2STAR said:

The Alt/Az mount of the evo 9.25 works very well with the Atik Infinity Mono or OSC, it will track easily for 120 secs with no star trails & decent images can be had,although not as good as with using a dlsr & eq mount. so maybe your camera is not the best suited for an Alt/Az mount.( unless you fit a wedge)

The main issue with the Evo is the Nexstar HC obtaining good initial alignment and you will find it is a very debated issue on what procedure works and what  does not, there are many many articles on SGL & CN so good luck.

I do have a wedge fitted, the HD Pro heavy duty one. I also have Starsense and have been using a new version of the firmware which fixes a bug with polar alignment. So far I am having good results, albeit after a lot of experimenting. I'm confident that I will be able to get good results after I get more familiar and quicker with the equipment. 

[2STAR]

Great to hear, it takes some patience but one good session and we forget all the poor nights !!!, how do you rate Starsense for backyard alignment, I heard it can be hit and miss ?, I have toyed with the idea of getting it for a while now.

Eric

[DoubleScoops]

2 hours ago, 2STAR said:

Great to hear, it takes some patience but one good session and we forget all the poor nights !!!, how do you rate Starsense for backyard alignment, I heard it can be hit and miss ?, I have toyed with the idea of getting it for a while now.

Eric

For Alt-Az use I rate Starsense very highly. Even with scattered cloud blowing over I have obtained excellent alignment. The one-off Centering required, to calibrate the install position of the camera, is something I *have* had issues with. I didn't seem to match my expectations with regards to accuracy, but I'm not giving up and will try to get better results. There was a polar alignment bug when using the wedge which meant that I had to swap back to the Nexstar handset to do the polar bit, then back to the Starsense one to carry out a 2nd auto alignment. There is an imminent firmware release which will fix this issue, it is being beta tested at the moment.

Would I get Starsense now knowing what I have found out about it? definitely yes.

[ollypenrice]

Regarding your question about the EP versus camera focus, I'd say that most of us regard removing the camera as anathema. I would never do that. I do everything through the camera after an intial star alignment by eye. On my widefield rig I can do this just by sighting along the tube rings to the alignment star and be sure it's going to be on the chip. On my hi-res setup the field of view is far smaller so I use a red dot finder and then a well-aligned finder scope to put the star on the camera chip. From there on it's all-camera. With the alignment star focused (using a Bahtinov Mask) I then centre the stellar image on the PC's virtual crosshair, synch the mount onto that, then slew to my target. The camera never comes out. This is better from the point of view of flats, camera orientation, cleanliness and time saving.

Do you know the importance, on an SCT, of making the final focus a 'push' of the mirror up the tube? On my (visual only) 14 ich Meade that means turning the focus knob anti clockwise. If you make your final focus a 'pull' the mirror may not come all the way back at once but settle a little further over time, throwing out your focus.

Olly

[Star101]

Thanks for that tid bit on the end Olly, I have always wondered why, sometimes, my SCT drops out of focus and other tims stays put! I will remember to do this from now on.

 

Doublescoops, Welcome to the rabbit hole $$$ of Astrophotography. 

[Demonperformer]

5 hours ago, ollypenrice said:

Do you know the importance, on an SCT, of making the final focus a 'push' of the mirror up the tube? On my (visual only) 14 ich Meade that means turning the focus knob anti clockwise. If you make your final focus a 'pull' the mirror may not come all the way back at once but settle a little further over time, throwing out your focus.

Maybe a silly question ... you say that on your scope it is anti-clockwise. Does this mean other scts might be different? Leading to a potentially even sillier question ... how does one tell which way is push and which way is pull? [I would have thought that clockwise was 'screwing in' and therefore 'pushing' the mirror up the tube, but that is obviously wrong]

Thanks.

[ollypenrice]

3 hours ago, Demonperformer said:

Maybe a silly question ... you say that on your scope it is anti-clockwise. Does this mean other scts might be different? Leading to a potentially even sillier question ... how does one tell which way is push and which way is pull? [I would have thought that clockwise was 'screwing in' and therefore 'pushing' the mirror up the tube, but that is obviously wrong]

Thanks.

I'm afraid I don't know. I've never taken a Meade SCT mirror sled to bits, nor do I know how the others work. I'm confident, though, that on the Meades the final focus should be anticlockwise = up. Even for visual observing I can see a more positive 'coming to focus' in the anticlock direction. Some SCT owners report no difference, some report equally crisp arrival at focus in each direction. Some are firmly convinced by the 'anticlock' theory. The state of the mechanism and its grease probably has a lot to do with it. If you take out the visual back you should be able to see which way your mirror moves.

Olly

[newbie alert]

I'm sure you will get many years of amazing views with the scope and other toys to annoy the wife with (love that statement)

I have a 236m myself and use it with my 8 inch..even though you're right in saying it's a ccd it's aimed at the planetary side as it won't do long exposures,more high frame rate video (lucky imaging

As for the focussing not sure what ep size the focus point is but I'd guess at around 6mm so yes it's going to be a long long wind from a 40mm or 20 something..what capture software are you using with it? If you near on max out the gain makes life a little easier to find the target and then adjust to focus..also lots seem to think starsense is a polar alignment aid,It's a star alignment aid which are 2 different things..yes it has the ASAP feature on the handset but so does the nexstar+ which isn't really accurate enough for dso imaging..fine for planet imaging and visual but needs a bit more accuracy for dso and long exposure as that will highlight any flaws in your PA 

[ollypenrice]

2 hours ago, newbie alert said:

I'm sure you will get many years of amazing views with the scope and other toys to annoy the wife with (love that statement)

I have a 236m myself and use it with my 8 inch..even though you're right in saying it's a ccd it's aimed at the planetary side as it won't do long exposures,more high frame rate video (lucky imaging

As for the focussing not sure what ep size the focus point is but I'd guess at around 6mm so yes it's going to be a long long wind from a 40mm or 20 something..what capture software are you using with it? If you near on max out the gain makes life a little easier to find the target and then adjust to focus..also lots seem to think starsense is a polar alignment aid,It's a star alignment aid which are 2 different things..yes it has the ASAP feature on the handset but so does the nexstar+ which isn't really accurate enough for dso imaging..fine for planet imaging and visual but needs a bit more accuracy for dso and long exposure as that will highlight any flaws in your PA 

 

When you say, 'As for the focussing not sure what ep size the focus point is but I'd guess at around 6mm so yes it's going to be a long long wind from a 40mm or 20 something' I suspect you are aiming to compare the field of view in a 6mm eyepiece with the field of view of the camera? (If I'm wrong, forgive me.) In truth the field of view in the eyepiece and the available field of view in the camera are entirely unconnected with the point of focus. You could find an eyepiece which gave about the same FOV as that captured on the chip (bearing in mind that EPs are round and chips are rectilinear) but the focuser would be in radically different positions when sharp for the camera and sharp for the EP even with comparable fields.

Olly

.

[newbie alert]

Yes olly..comparing the fov..well guessing really as I don't own a 6mm..might be more or less