Made a finder-guider... Focus problems...

[Alveprinsen]

Ok, so.. Ordinarily I've guided using my Orion Starshoot Autoguider through a 500mm FL Skywatcher refractor.

BUT - I will be using my Skywatcher Explorer 200PDS next week, and I want to mount a lighter guiding scope on it.

So - I butchered one of the finding scopes I had lying around, picked up an on T-adapter, and modified it so that it would slide smoothly in and out of the guilder scope body.

But there is one problem. I just tested it using an ordinary web-cam, and I can only get focus on stuff that is closer than 4 meters to me. If I push it as far into the barrel as I can, I can focus on stuff a few meters in front of me. If I pull it out - the focus moves closer.

So, I suspect that in order to get infinite focus with it, I will have to push the camera far far into the finder scope body.

Does anyone else have any experience with making finder-guiders?

Sincerely, Alveprinsen.

[triton1]

Don,t you have to remove the lense from the webcam?

[knobby]

Just made one myself with a Skywatcher 50 mm finder. I had to trim about 10mm in length to achieve focus ... Or mount the camera direct to the tube so was in effect closer

[Alveprinsen]

Just made one myself with a Skywatcher 50 mm finder. I had to trim about 10mm in length to achieve focus ... Or mount the camera direct to the tube so was in effect closer

Looking good!

Here's mine:

I tried with a web-cam first, and failed at focus. Then I went down to the observatory and dismounted the guiding camera and tried that, and managed to aaaalmost achieve perfect focus due to the chip being closer than that of the webcam.

Gonna take the sliding-tube I made at work yesterday back to work today and shave off just a little.

Seems I got this solved.

Nice looking setup btw Red.

[Alveprinsen]

Don,t you have to remove the lense from the webcam?

Indeed you do.

[knobby]

Good luck ... And before anyone mentions flexure on my set up

[Thalestris24]

Hi

If you put your finder back together and focus it on infinity, you can measure the distance between the objective and the first lens in the eyepiece. That will be the distance you need between the objective and the image sensor plane.

Hth

Louise

[Alveprinsen]

Hi

If you put your finder back together and focus it on infinity, you can measure the distance between the objective and the first lens in the eyepiece. That will be the distance you need between the objective and the image sensor plane.

Hth

Louise

I see.

Well, in order to get focus with the guiding cam, I need to move the chip closer than the secondary lens in the reticule previously attached.

What I am wondering now is:

1. What is the Focal length? From googling around, I'm being led to believe the 9 x 50 finder is at a 180mm FL.

2. Will the Orion Starshoot Autoguider camera guide correctly using this finder scope? I am reading mixed epxeriences on this on various forums I've googled.

Some say the manage to achieve 3 minute exposures, others say a 9 x 50 finder scope should be able to guide for focal lengths up to at least 1000mm without problems.

In other words... Should I rather go for a Skywatcher Startravel 80 instead and be absolutely sure its enough? Up until recently I've been guiding with the Startravel 102, but I feel its too heavy to piggy-back on the 200PDS. Which is the only reason why I've now made a finder-guider.

Sincerely, Alveprinsen.

[Thalestris24]

Hi

Yeah, I think the focal length of the objective is about 180mm (checking mine). I suspect your problem is the backfocus of your autoguider. I did a quick search and came across this:

http://stargazerslounge.com/topic/217423-how-to-attach-autoguider-to-finderscope/

Not sure how that was sorted in the end.

Lots of people happily use ST-80's as guide scopes but they are heavier than a finder (lighter than an st-102!) and obviously have a narrower fov. A finder-guider should be ok for your setup.

All the best

Louise

[Alveprinsen]

Hi

Yeah, I think the focal length of the objective is about 180mm (checking mine). I suspect your problem is the backfocus of your autoguider. I did a quick search and came across this:

http://stargazerslounge.com/topic/217423-how-to-attach-autoguider-to-finderscope/

Not sure how that was sorted in the end.

Lots of people happily use ST-80's as guide scopes but they are heavier than a finder (lighter than an st-102!) and obviously have a narrower fov. A finder-guider should be ok for your setup.

All the best

Louise

Thanks.

I just put in a 2x barlow as well. FOV is narrow as hell, and I suspect the F ratio plummets if I use it...

I would prefer not having to use a barlow, but if it is as you say - my 180mm FL finder-guider should be able to guide my 1000mm FL scope, thats good enough for me. As long as it can guide 10 minute exposures flawlessly. If not, I guess I will need to install the barlow or get one of those ST-80's....

[Thalestris24]

Thanks.

I just put in a 2x barlow as well. FOV is narrow as hell, and I suspect the F ratio plummets if I use it...

I would prefer not having to use a barlow, but if it is as you say - my 180mm FL finder-guider should be able to guide my 1000mm FL scope, thats good enough for me. As long as it can guide 10 minute exposures flawlessly. If not, I guess I will need to install the barlow or get one of those ST-80's....

Hi

You really don't want to add a Barlow - a x2 will double the focal length and the focal ratio! You'd go from F3.6 to F7.2 needing 4x the guide star exposure!

You might try undoing the front of the guider and removing the focus locking ring and then screwing the objective holder back. That would bring the objective closer to the sensor. You would have to find some way of keeping the objective from moving - maybe some insulating tape. I had to do that with my old qhy5l-ii which had a long nosepiece.

Louise

[Alveprinsen]

Hi

You really don't want to add a Barlow - a x2 will double the focal length and the focal ratio! You'd go from F3.6 to F7.2 needing 4x the guide star exposure!

You might try undoing the front of the guider and removing the focus locking ring and then screwing the objective holder back. That would bring the objective closer to the sensor. You would have to find some way of keeping the objective from moving - maybe some insulating tape. I had to do that with my old qhy5l-ii which had a long nosepiece.

Louise

Yeah, I figured that. I just read in another post in some other forum about a guy who added a barlow to his finder for better accuracy. But if it is as you say, that the 180mm FL finder scope will guide 1000mm FL imaging scope just fine - I'm down with that.

I wonder though... if Astro Tortilla will image with the Orion Starshoot Autoguider. Since I will be now actually aligning my finder scope with my imaging scope - it could come in quite handy.

[Thalestris24]

Hi

Astrotortilla plate solves from your main imaging camera - the guide setup is secondary to that. What imaging camera do you have?

There is a sticky thread on here about using PHD and discusses pixel scales etc.

http://stargazerslounge.com/topic/188777-phd-guiding-basic-use-and-troubleshooting/

There is also an Astrotortilla thread.

Louise

[Sandancer10]

I'm new to auto guiding too and originally thought of using my ST80, but I found it too heavy on the mount. I bought the QHY5-ii and 9 x 50 SW finderscope and after 2 weeks of trying I finally managed to get focus. I even took my kit to  the Astro club and they spent 2 hours trying to no avail. So I would say even though you may find you can't focus it may come right if you fiddle with it long enough.   

[Alveprinsen]

Hi

Astrotortilla plate solves from your main imaging camera - the guide setup is secondary to that. What imaging camera do you have?

There is a sticky thread on here about using PHD and discusses pixel scales etc.

http://stargazerslounge.com/topic/188777-phd-guiding-basic-use-and-troubleshooting/

There is also an Astrotortilla thread.

Louise

Yeah, however - I'd like Astro Tortilla to use the guiding cam for plate solving since I am using one computer for guiding and go-to with Stellarium, and another for imaging with Backyard EOS.

I am using a enhanced and cooled Canon EOS 600D from CentralDS in Korea.

My imaging computer does not have a connection to the mount, so Astro Tortilla would not be able to slew the mount. But seeing as the finder-guider and the main scope will now be more or less perfectly lined up with eachother - I could use Astro Tortilla to center the object for me, and I could fine-tune it myself by slewing slow-mo and snapping a couple of test images with the main scope afterwards.

[Thalestris24]

Hi

Um, why two computers?

Louise

Edit: I think you'd need BYEos or APT to interface with AT - it has to get the image from somewhere. That might cause problems if you're also trying to use PHD to access the camera

[Alveprinsen]

Hi

Um, why two computers?

Louise

Edit: I think you'd need BYEos or APT to interface with AT - it has to get the image from somewhere. That might cause problems if you're also trying to use PHD to access the camera

Because one of them is not strong enough to run ASCOM, Stellarium, Stellariumscope, PHD Guiding and Backyard EOS at the same time.

And I cannot afford to buy yet another laptop just so I can use Astro Tortilla.

I'd have to fork up at least 470 GBP for a suitable laptop to run all that stuff.

EDIT: Hmm, found a Acer Aspire E1-510, 4 Gig RAM, Quadcore Celerom processor.... If I beef that up with another 4 gigs of RAM, I guess I could use that instead of two comps. It only cost like 235 GBP anyways... I guess I could treat myself... What a little more debt? But a drop in the ocean...

[Thalestris24]

Hmm

I'd have thought any pc or laptop would be capable of managing the above. You can always exit Stellarium once you've found your target and are guiding. Ascom in itself doesn't do much. Stellarium can be quite demanding but you can dismiss it if you're not actively using it. BYEos, I don't know, but you are only really using it when acquiring an image. Phd is quite busy and it needs a fair bandwidth to continuously download the guide images. Still, it's your decision! Astrotortilla is quite demanding - but only when you're actually plate solving. As I say, I don't think you'd be able to use it with the guide cam the same time as phd.

Louise

[Alveprinsen]

Hmm

I'd have thought any pc or laptop would be capable of managing the above. You can always exit Stellarium once you've found your target and are guiding. Ascom in itself doesn't do much. Stellarium can be quite demanding but you can ...

No matter... I just ordered a new laptop and 8 gigs of RAM.

I will be plate solving in notime!

[Thalestris24]

No matter... I just ordered a new laptop and 8 gigs of RAM.

I will be plate solving in notime!

Oh my, that was very impulsive of you! I usually try to avoid spending lots of money late at night... Which one have you ordered? I have to get myself a laptop. I've been mulling over which one to get for several months now!

Louise

[Alveprinsen]

Oh my, that was very impulsive of you! I usually try to avoid spending lots of money late at night... Which one have you ordered? I have to get myself a laptop. I've been mulling over which one to get for several months now!

Louise

Impulsive is my middle name...  How do you think  I got into Astronomy in the first place...

I bought a Acer Aspire E1-510 and a RAM upgrade of 8 gigs. That should be sufficient to run all the software I need.

Now I just hope Windows 8.1 wont give me any software and driver trouble with ASCOM etc...

[thanders]

Finder guider: 8x50 + SSAG

I have made myself this auto guider. I had to shorten the finder tube 3mm to get focus. The focal length is approx 180mm.

I have been guiding my 1800mm Maksutov-Cassegrain with very good result. Nice, round stars with 600s exposures.

Works like a dream.

/T

[Thalestris24]

Impulsive is my middle name...  How do you think  I got into Astronomy in the first place...

I bought a Acer Aspire E1-510 and a RAM upgrade of 8 gigs. That should be sufficient to run all the software I need.

Now I just hope Windows 8.1 wont give me any software and driver trouble with ASCOM etc...

Hopefully 8.1 64 bit should be ok though not all astro apps are available in 64 bit but should be ok anyway. Everything runs ok on a Win7 64 bit system I have. 

I'm still trying to decide on a laptop. Might manage to finally make a decision this week

Edit: btw how is your cooled 600d? Can I ask how much they cost?

Louise

[Alveprinsen]

Hopefully 8.1 64 bit should be ok though not all astro apps are available in 64 bit but should be ok anyway. Everything runs ok on a Win7 64 bit system I have. 

I'm still trying to decide on a laptop. Might manage to finally make a decision this week

Edit: btw how is your cooled 600d? Can I ask how much they cost?

Louise

I havent had the chance to actually use my cooled 600Dmuch. I've only used it for a botched attempt at NGC7023.  but as far as my experience so far goes - it works like a charm.

I must say, CentralDS has been extremely accomodating. And I cannot stress the word "extreme" enough. When I ordered it, I was told production time was 2-3 weeks, + shipping. After barely 3 weeks I got a notice in my mailbox that a package from South Korea was waiting for me at the post office. After having used the camera a couple of times, it stopped cooling. something wrong with the peltier system. I sent it back, and they fixed it and returned it to me after only two days! They even refunded my shipping cost...

In room temperature it cools down to -5 C. Outside in an ambient temperature of about +5 degrees C it cooled down to like -18 C. It will probably cool down to like -25 C when the cold sets in. 

Whats really cool about it is that I can connect it directly to a 12V source if I dont want to use the AC adapter. Also, there is a port for remote shutter, so if I like - I can use a computer to get focus, then disconnect computer and use my remote shutter release to run the exposures.

Price is listed on their webpage. I went for the full package.

[Alveprinsen]

Finder guider: 8x50 + SSAG

I have made myself this auto guider. I had to shorten the finder tube 3mm to get focus. The focal length is approx 180mm.

I have been guiding my 1800mm Maksutov-Cassegrain with very good result. Nice, round stars with 600s exposures.

Works like a dream.

/T

Awesome stuff... you just made my da.. uhm, night Sir.

I wonder if it could guide my 2700mm Maksutov.... I got a bigass OAG, but ... FOV is soooo narrow with it. hehe