Focus / Target problems - advice please!

[Tommohawk]

Hi. I'm making very slow progress with astrophotography. Have recently got a polar scope and this defintiely helps and is easier to use than I thought. I have big problems having to re-site multiple times due to trees and house obstructing the view, so being able to polar align quickly is a priority. I was trying to get a good result with M31 for starters, but this now disaapears behing the house after 7pm so no real time to get set up etc.

So - I currently have quite a good view of M82/M81 and thought I'd try and photo that, and maybe get the supernova if its still visible. Here's the problem.

My technique with M31 and M42 has been to locate in finderscope, then centre up in main scope with 25mm EP, then set tracking, remove EP and fix camera - Nikon 3200. I can then refocus using the LCD screen, which is made easier by using the screen zoom function. I have had all sort of tracking issues, but leaving that aside this works OK.

The problem with M81/82 is that there doesnt seem to be a star thats bright enough in the camera view to be visible on the screen. If I slew off to one side to find a brighter star, I can then focus nicely, but cant then locate the target.

I cant help but think I'm missing something here - any idea please? I cant connect this camera to a laptop. Do you think if I hooked up a Canon to the laptop, the image would be bright enough to see?

I only tried this one time last night, and then cloud cover interuppted things - maybe I just didnt have enough time.

[PorkyB]

Focus camera on something bright - lock the focusser - put the eyepiece back in and slide it in until it's in focus, don't adjust the focuser - find your target - put camera in - fine tune focus if you can find anything to focus on (and you probably can if the focus is already good) - and off you go

a parfocal ring and an eyepiece extender may help

[melsky]

Sometimes it's surprising what you can see through the camera's eyepiece so after you've focused up on a nearby star try that instead of using the LCD, often works for me.

Mel

[Leveye]

You really want to get a laptop or phone/tablet app thats connected to your mount which i am taking for granted in motorized. After a good alignment you then use that program to get you pointed in the right direction. Take a few test pictures and adjust accordingly using live view and you're off. I like CDC myself.

[Tommohawk]

Thanks for express comments!

Focus camera on something bright - lock the focusser - put the eyepiece back in and slide it in until it's in focus, don't adjust the focuser - find your target - put camera in - fine tune focus if you can find anything to focus on (and you probably can if the focus is already good) - and off you go

a parfocal ring and an eyepiece extender may help

Now that's a good idea! Will have to give it a try. The problem is that in order to connect the camera, I need to unscrew release the outer housing and unscrew the adapter thingy. Need to have a look if the spare 2" adaptor has the same fitting - would save having to swap over. So quite a kerfuffle, and might not realign exactly. As you say, would be close and then maybe could find something bright enough to fine tune.

Sometimes it's surprising what you can see through the camera's eyepiece so after you've focused up on a nearby star try that instead of using the LCD, often works for me.

Mel

I did try that, but couldnt see a sausage.

What do you think about the idea of hooking up to a laptop? Would that screen show the image better? Cant do thins til I upgrade camera, but that is on the cards.

[Tommohawk]

You really want to get a laptop or phone/tablet app thats connected to your mount which i am taking for granted in motorized. After a good alignment you then use that program to get you pointed in the right direction. Take a few test pictures and adjust accordingly using live view and you're off. I like CDC myself.

Pretty much a newbie, so not sure whats required for this - could you expand please?

[Alien 13]

I dont know if the Nikon live view is different but if i set iso to 1600 and shutter to 30 seconds and zoom in one click with my camera i can see very faint stars and i use these to focus.

Alan

[Stargazer33]

Once you have found your target take a test shot of say 30 seconds. Bring the image up on screen and zoom in on a star to check focus. If it's not focused, adjust in one direction and take another shot. If this improves things carry on in that direction until you get focus. If it makes things worse then go back in the opposite direction. Takes a little longer but is cheaper than buying a new camera and laptop!

[Kropster]

If you use a Bahtinov mask, you should get some stars on a 30 sec exposure.

Just keep making small adjustments then taking another exposure until the Bahtinov pattern is spot on.

Or.... Bahtinov on a bright star nearby..then move  scope back roughly to point you want to shoot, take 30 sec exposure to check where it is pointing and adjust position.

If you can align the finder scope as accurately as possible, that will be a great help in positioning after focusing on a bright star.

[Tommohawk]

I dont know if the Nikon live view is different but if i set iso to 1600 and shutter to 30 seconds and zoom in one click with my camera i can see very faint stars and i use these to focus.

Alan

Do you mean just using live view, or do you take an exposure and then check? I would have thought Liveview view on LCD screen would be the same irrespective of ISO settings etc

Once you have found your target take a test shot of say 30 seconds. Bring the image up on screen and zoom in on a star to check focus. If it's not focused, adjust in one direction and take another shot. If this improves things carry on in that direction until you get focus. If it makes things worse then go back in the opposite direction. Takes a little longer but is cheaper than buying a new camera and laptop!

Like the idea of anything that doesnt entail further outlay! But I always seem to be limited for time. Either the clouds come over, or one of the kids decides to try out their new disco lights, or the phone ... etc!

If you use a Bahtinov mask, you should get some stars on a 30 sec exposure.

Just keep making small adjustments then taking another exposure until the Bahtinov pattern is spot on.

Or.... Bahtinov on a bright star nearby..then move  scope back roughly to point you want to shoot, take 30 sec exposure to check where it is pointing and adjust position.

If you can align the finder scope as accurately as possible, that will be a great help in positioning after focusing on a bright star.

I havent tried a mask yet. Generally I get good focus, by simply zooming on liveview image. I like the point about the finderscope - maybe if I just get that aligned absolutly spot-on, I can refix using just the finder.

Thanks all for comment.

Anobody use the Canon + liveview on laptop? Does this give brighter image than on camera screen?

[Alien 13]

Do you mean just using live view, or do you take an exposure and then check? I would have thought Liveview view on LCD screen would be the same irrespective of ISO settings etc

Like the idea of anything that doesnt entail further outlay! But I always seem to be limited for time. Either the clouds come over, or one of the kids decides to try out their new disco lights, or the phone ... etc!

I havent tried a mask yet. Generally I get good focus, by simply zooming on liveview image. I like the point about the finderscope - maybe if I just get that aligned absolutly spot-on, I can refix using just the finder.

Thanks all for comment.

Anobody use the Canon + liveview on laptop? Does this give brighter image than on camera screen?

The apparant brightness of the image on my live view screen increases with the iso setting so i can view very faint stars even nebulosity direct so have no need to take a test exposure i have found that if i focus on a very dim star it is almost like a switch where is either in view or vanishes so its a very precsice method for me.

Alan

[Tommohawk]

The apparant brightness of the image on my live view screen increases with the iso setting so i can view very faint stars even nebulosity direct so have no need to take a test exposure i have found that if i focus on a very dim star it is almost like a switch where is either in view or vanishes so its a very precsice method for me.

Alan

Well thats worth knowing for sure! I'm looking for a Canon right now, so good to know. I somehow doubt that will apply with my Nikon though, but definitley worth checking out - thanks for the tip.

[Russe]

If you can connect your mount to EQMOD, you could use AstroTortilla to get spot on on target.

Focus your camera on a bright star with a Bahtinov mask. Slew to your target. Open AstroTortilla, solve image and let it iterate until it is satisfied. Then image.

[Russe]

The camera would have to be connected to your laptop too for this method, I'm afraid.

[Russe]

http://sourceforge.net/p/astrotortilla/home/Home/

Astrotortilla

[Russe]

http://eq-mod.sourceforge.net/

EQMOD

[Russe]

Camera control with APT:

http://www.ideiki.com/astro/

[PorkyB]

 I need to unscrew release the outer housing and unscrew the adapter thingy. Need to have a look if the spare 2" adaptor has the same fitting - would save having to swap over. So quite a kerfuffle...

Things get easier if you have the SW coma corrector as this attaches to your camera and presents a 2" fitting to your scope.  Makes it much quicker and more accurate to swap between camera and eyepiece.

[Tommohawk]

Thanks Russe for those links - need to check them out when there is a moment.

Things get easier if you have the SW coma corrector as this attaches to your camera and presents a 2" fitting to your scope.  Makes it much quicker and more accurate to swap between camera and eyepiece.

Thats an excellent idea - didnt think of that. Shame its 0.9x though - for most targets I need more mag. Do you know if I can barlow this? Presumably must be possible - will it still correct coma I wonder?

[PorkyB]

...Do you know if I can barlow this? Presumably must be possible - will it still correct coma I wonder?

I've not tried, yet.  My experiments with a barlow were not very successful, maybe because you need a much longer exposure (4 times as long for a 2x barlow), maybe because the longer focal length and exposure times showed up the limitations of my mount, or maybe because it was a rubbish barlow.

It would need to be a 2" barlow to take the coma corrector.

[Tommohawk]

Follow on:

Well - I had a pretty good on 26th Feb.  Used a combination of techniques, but key things were:

Used polar scope for good aligment - everyone says its neccesary for good tracking, and guess what..... theyre right.

Located M82 after a bit of a performance - its funny how you develop pattern recognition for clusters of stars and use them to navigate. Having got M82 in my sights, I set tracking, and then swapped to camera. I definitely cant see anything in the LCD screen for this target - I tried the trick of increasing the ISO, but on the NIkon is doesnt seem to affect Liveview.

I knew more or less where focus should be so set ISO to 1600 and did 6 second exp - enough to get an image and then did a succession of shots fine tuning a I went. Ended up with a focus that was pretty good and shots 20 lights +darks + bias all at 1600 ISO.

Not being completely convinced about original focus, I refocussed by noting carefully the Dec setting, then adjusting Dec till I found a star that showed in the Liveview, focussing carefully with screen mag at maximum, and then reset to original Dec setting. RA tracking left running throughout. A couple of short trial pics to re-align, and then re-shot with ISO800. As a focussing method, this proved to be the best.

All this ended up about 11.30, work next day, cloud cover due any minute, so I was well pleased. In fact it all seemed to good to be true. And it was.... I'd been fiddling with the camera settings, and left it on JPEG instead of RAW. That said, the JPEG images were very pleasing

From here on it gets very confusing - lot of processing issues. Long story short - the JPEG images looked pretty good, especially after processing. I did some RAW shots a couple of night later, and couldnt get such a good result. I will post the images and the related processing queries seprately so as not to muddle this thread. Thanks to all for advice - all very helpful and I think I now have a good method for aligning and focussing on objects which are too dim for the LCD screen to show.

[Kropster]

I would still recommend a Bahtinov mask for focussing on a bright star... it just removes any guesswork.

Having got one myself, I wouldn't use any other method now.

[Tommohawk]

I would still recommend a Bahtinov mask for focussing on a bright star... it just removes any guesswork.

Having got one myself, I wouldn't use any other method now.

I'm sure youre right. It's just that there are so many things to try and get familiar with. I'm still getting used to the scope - not convinced about my collimation, and the cameras new, as is the whole processing thing.

The other thing is I dont have a dual speed focusser - so right now that seem to  be the limiting factor.

[mitchelln]

I used to have exactly the same problems as you are describing. Does your EQ3-2 have PAE correction and the save and recall functions?

I've found my mount is simply not accurate enough even after a careful 2 star align. However, all is not lost as someone on this forum pointed me to the PAE correction facility. It is incredibly useful and transforms the accuracy of the mount. I do wish Skywatcher would write decent manuals! Thanks to the SGL member (can't remember who!) for highlighting it.

So I use PAE to get the mount to recalibrate to a nearby object. Dubhe is a good candidate for M81/82. From then on the mount will switch between Dubhe and the galaxies accurately. I then focus on Dubhe using my Bahtinov mask and then slew back to M81/82.

Also, once the mount is pointing where I want, I save the position. This is especially useful if I want to capture both galaxies in the same shot rather than point directly at one or the other.

This approach has saved me so much time and frustration You will struggle a bit with a single speed focuser though.

By the way, the Baader coma corrector does not affect focal length or field size. It also gives you an incredibly low profile 2" mount when coupled with a T2 adapter

[Tommohawk]

I used to have exactly the same problems as you are describing. Does your EQ3-2 have PAE correction and the save and recall functions?

I've found my mount is simply not accurate enough even after a careful 2 star align. However, all is not lost as someone on this forum pointed me to the PAE correction facility. It is incredibly useful and transforms the accuracy of the mount. I do wish Skywatcher would write decent manuals! Thanks to the SGL member (can't remember who!) for highlighting it.

So I use PAE to get the mount to recalibrate to a nearby object. Dubhe is a good candidate for M81/82. From then on the mount will switch between Dubhe and the galaxies accurately. I then focus on Dubhe using my Bahtinov mask and then slew back to M81/82.

Also, once the mount is pointing where I want, I save the position. This is especially useful if I want to capture both galaxies in the same shot rather than point directly at one or the other.

This approach has saved me so much time and frustration You will struggle a bit with a single speed focuser though.

By the way, the Baader coma corrector does not affect focal length or field size. It also gives you an incredibly low profile 2" mount when coupled with a T2 adapter

My mount is not synscan at all! Its dual motorised but thats all. However, its a good point that realigning after focussing would be easier with Synscan.

I may upgrade the focusser to dual speed. Also that CC looks good - I'd assumed they were all 0.9x or similar. All lots of £ though! TBH  think my first priority would be to upgade the whole mount.