Focus

[imbecile]

I have a friend who has bought a goto Cassegrain telescope with a lot of extras and I'm trying to help set it up. The light path comes out the bottom of the scope and there is an elbow to enable more comfortable viewing.

Step 1: I stuck an eyepiece in there and managed to get it manually pointed at Jupiter using the handheld controller and got it into focus. Tick.
Step 2: Got the 3 star alignment working so that I could slew round and track Jupiter automatically. Tick.
Step 3: Got the controls to work from the laptop rather from the hand controller. Tick.
Step 4: The Phillips webcam with telescope modification slotted in nicely and I could see the Moon on the laptop. Tick.
Step 5: Tried to focus the Moon on the webcam but no joy. The focus would come in and go out the other side, but at no time was the Moon actually clear on the webcam image. Bum.
Step 6: With the best focus on the Moon I could get then pointed the webcam at Pleiades but the screen was totally blank. Nuffink. Tried a few more stars but still zilch.

So here are my stupid questions.

1. What gives with the focussing? It's definitely not an issue of focus distance to the webcam CCD cos the focus comes in from blurry, through slightly less blurry and then goes out the other side into total blurriness as I move the focus knob. Any ideas?

2. Why can't I see any stars in the webcam, only bright objects like the Moon? Is this webcam too insensitive or is there some sort of gain enhancement I could try? Or is it because of the focus problem (all the stars are there on the screen but are smeared out into blurry splodges)?

TIA

[michael.h.f.wilkinson]

If you are focusing with the standard focusing knob of the typical SCT, focus is VERY tricky. I think I am going to try a Bahtinov mask (focus on bright star with mask, and move to object).

I also found getting objects on the tiny chip of a webcam VERY hard. I solved my problems with a flip-mirror: attach an EP to one port and the webcam to the other. Centre object with EP, flip mirror, and the object is on the camera.

[Cornelius Varley]

Focusing can be quite tricky when imaging. You"ve noticed that you can go from one one side of out of focus to the other very quickly. What you need to do is slow down a bit when you get near to focus and then carefully tweak the focuser until you get the best focus you can. It may not snap into focus due to atmospheric conditions bouncing the image around so you just need to get the best you can, usually focusing on the limb of the moon works best. Unfortunately imaging stars with a standard webcam not possible. You need longer shutter speeds than a webcam can provide.

[leelee970]

I don't own a Cassegrain telescope so thins may not apply.

set the webcam to fully auto. then try to focus on the moon.

I'm not sure you'd need or should have the diagonal mirror attached.

you'll have a hard job picking up stars with a webcam, but it is possible. Deep sky object require longer exposure times which the standard webcam can't give.

[imbecile]

Hmm well his plan was to set it up so that from the warmth of his house he can operate the telescope outside and view the images. I guess this isn't really feasible. Not sure how I'm going to break it to him that he's dropped well over a thousand quid on a hobby he'll probably never take up (unless he's willing to go outside in the cold).

[Russe]

Wait, wait, wait! Don't throw in the towel yet!

A webcam is really just the first step in the game of astrophotography! It takes a lot of commitment and postprocessing to achieve nice pics.

With no camera will you be able to view the nightsky on a screen in HD. The only way forward would be videoAP for that.

If your friend has a permanent setup he would still be able to enjoy astronomy with a minimum of cold feet. A webcam though, will not work for that... At least a DSLR with a live view option would make things much more easy. But this as well will leave you with quite dim objects on the screen that will require postprocessing with an imaging software to make it "brighter".

If that's smth that your friend is interested in, then sitting in the warmth of his room becomes a possibility. Just recently we had 2 very clear nights on the weekend but I was on call during the nights. As I don't have a permanent setup, I put my scope outside, polar aligned it, focused it (Bahtinov mask - Canon 450D), logged my computer into my logmein.com account and went to work. From there I could control my rig via any computer logged into logmein.com and had full control.

For that I use several programmes: Stellarium, stellariumscope, EQMOD, APT, PHD.

Calibration frames will still have to be taken for this sort of thing (Darks, Flats, Bias). But that takes things a bit too far for now.

Does that help a bit?

A webcam really needs you to be outside with the scope. And you can only image planets or the moon unless you'd have a modified webcam for long exposures.

[Astrosurf]

If the seeing's poor and the Moon wobbles a lot, then focusing is hard but not impossible. I have the benefit of having an autofocuser so my scope doesn't wobble when focusing and it's very accurate. I don't know if that's something you can get for yours. Mine is a Skywatcher. A guy on here used a sort of clip, like a large clothes peg, that he attached to his focuser which created a lever that made fine focusing easier.

What capture sw are you using? I use SharpCap which is great. Get the focusing as close as you can, get the settings on your capture sw so that you can see details OK (not too bright), capture a vid and then stack in Registax. The post processing in Registax can bring out so much detail compared to what you can see in the vid it can be a real surprise!

Do you have any processing sw like GIMP or Photoshop?

Alexxx

[brantuk]

"Hmm well his plan was to set it up so that from the warmth of his house he can operate the telescope outside and view the images. I guess this isn't really feasible."

Incorrect I'm afraid. Many people do this - in fact astro photography rarely requires presence at the telescope and can be done entirely remotely. What has to happen first though is that he needs to learn how to do it - it's a skill that demands a lot of attention and practice and has a steep learning curve. So some outside work is required during the initial stages.

Quite apart from the actual photography he'll need to know how to set the equipment up properly, and on top of that he'll need to learn to judge the "seeing conditions" and ascertain if any particular night is suitable for imaging (a skill in it's own right).

[imbecile]

Thanks for all the replies.

@brantuk: I won't be seeing him again until January but it'd be nice to be able to come to him with a solution that he can at least work on from there. He's very lucky to live in a small town with far less light pollution than where I live.

@Astrosurf: His telescope is a Celestron 6SE, the focus knob is very strange cos it has no stops. You can turn it in either direction until your hand becomes a blumming stump. The capture software he's using is sharpcap. I've taught him very basic gimp techniques. Haven't tried registax yet.

@Russe: I know he has a Nikon dslr but don't know which model. How was the image from your dslr viewable on the computer?

Quite frankly I'm sooooo glad I went for a cheap dobsonian cos I can be set up and viewing stuff when there is just a few minutes gap between clouds.

No astrophotography but I'm just starting out so who cares. Also I'm learning my way around the cosmos which is kinda cool.

[imbecile]

That's interesting. I wrote the word bl00dy (as in covered in blood) and the swear catcher on this site turned it into blumming. How very delicate.

[Russe]

delicate indeed

I use APT (astrophotography tool) for my Canon 450D and connect it via USB. But I've just looked at their page and they don't seem to support Nikon Cameras. Therefore, you gotta search for software support on this forum or start a new topic.

[m37]

There are kids on this site from time to time, although the bit of the focuser you turn to change focus also happens to be slang for a certain body part and gets filtered out!!!

Your friend can buy a focus motor, USB interface and 10m USB repeater for about £120. This allows you to focus from indoors without wobble and also can turn very, very slowly for fine focusing.

[imbecile]

Thanks for the further replies.

@Russe: I have a Canon dslr so I'll try to get that working before finding a Nikon based solution for my friend. Anyone know of similar s/w for Nikon?

@m37: I'm not really in a position to ask him to spend even more money, especially if I haven't got a clue if the setup will ultimately work. Besides, if I get him to buy stuff, I become obligated to provide indefinite support :-)

[m37]

Thanks for the further replies.

@m37: I'm not really in a position to ask him to spend even more money, especially if I haven't got a clue if the setup will ultimately work. Besides, if I get him to buy stuff, I become obligated to provide indefinite support :-)

I understand. Cheapest option for remote focus from the warmth of indoors is a servo from ebay (£5 ish) but this will require modifying to make it continuous as servos typically have a fixed range of motion. There are tutorials on the web and I did it successfully using various brackets and belts. It works just fine.

good luck with it.

[Johnboy]

Hi,

I find with my webcam the view on the laptop tends to take time updating. In other words I have to tweak the focus knob then wait a few seconds before the result appears on the screen. If I go to fast the view on the screen lags behind slightly. Turn the knob a little at a time and wait for the result to appear before turning again.

Regards

John

[CSM]

I have this setup and it takes brilliant images of the Moon.  I use WxAstrocapture and select the second option in the camera selection. Also with the Moon you may have to set it to 1/100 sec for the shutter speed and 10 fps  in order to see anything. And as has been said before, focusing does need care - just turn the knob a little at a time and allow it to settle down each time.. Have a look at my web site, in particular Beyond Reality and if you need any further help send me an email.

[Tinker1947]

I found when i first used my C11 the focuser needed a lot of care, I replace the fitted focuser with a Starlight Feathertouch, take about 5 minutes and give a 10-1 fine tuning option, its so much better FLO seem to be the cheapest place to buy from....

http://www.firstlightoptics.com/starlight-instruments-feathertouch/microfocuser-for-celestron-c11-sct-edge-hd.html

[brantuk]

With an Sct and just the standard focuser you need to focus the webcam as best you can. It will be a matter of manual adjustment till such time as he can afford a dual speed and/or motorised focuser. Planets and moon go in and out of focus constantly even when the focus is spot on. The variation is due to the seeing - even when observing the planet will appear to "wobble" or "boil" in the eyepiece.

What you are trying to do with a webcam is capture the precise instant when the seeing settles down and capture it in a single frame. The seeing does settle down periodically but only for a second or two if lucky. Run the webcam for 3-5 mins at a time and capture 5 or 6 thousand frames. Registax can then be used to stack the best ones to get the best set of frames.

Then you need to tart up the result in photoshop or similar processing software (get gimp if you want a  free one).

So don't worry about initial focus - just get it as good as you can