New Off Axis Guider

[Tim]

In my experience a mm or two either side of ideal has no significant impact on image quality or flatness with astrophotography. At least on scopes down to f4, I haven't tried faster than that yet.

There is even confusion in the measuring of the focal length of the cameras, and whether it should be from the silicon layer or the cover slip.

Certainly don't lose sleep over it, just get as close as you can to ideal and try it out.

If you need to micro adjust your rig, then the delrin spacers from Baader are the thing to get. They also help to stop adapters welding themselves together!

[Tim]

These are they, just the thing for adding 0.3mm -1mm to your imaging train

http://www.firstlightoptics.com/adaptors/baader-t2-delrin-spacer-ring-set.html

[axle01]

Seeing FLO doesn't ship to Australia where else can I get one.

Alan

[Zakalwe]

Anything that stops those b****y T threads from sticking together is A Good Thing in my book.

[FLO]

Seeing FLO doesn't ship to Australia where else can I get one.

The Australian equivalent to SGL is IceInSpace with over 12,000 members. I am sure they will be able to help regarding local suppliers

Steve

[axle01]

The Australian equivalent to SGL is IceInSpace with over 12,000 members. I am sure they will be able to help regarding local suppliers

Steve

Thanks Steve I will ask there.

Alan

[axle01]

http://www.optcorp.com/thin-off-axis-guider-m48-t2.html

Is this the same one.

Alan

[Tim]

No, that's the original TS one. I have used that one for a long time, but it is not as good as the one on discussion.

[axle01]

Thanks Tim, I wish I had seen your post 2hrs ago I just got one s/h from New Zealand, so is there much difference between the 2.

Alan

[Tim]

I upgraded mine thanks to a fellow moderator with some solder tipped screws. which helped it be more firm in use. You may also have to block off the gaps in the body with tape or something to prevent light leaking in. I also added allen bolts instead of thumbscrews after an incident with a falling camera, but aprt from that you should be fine with the TS guider

[axle01]

I upgraded mine thanks to a fellow moderator with some solder tipped screws. which helped it be more firm in use. You may also have to block off the gaps in the body with tape or something to prevent light leaking in. I also added allen bolts instead of thumbscrews after an incident with a falling camera, but aprt from that you should be fine with the TS guider

Thanks Tim when it gets here I will have a look at those suggestions.

[Tim]

In the past some have reported a little bit of flexure issue even when using an OAG. I have never noticed it myself, but the other night I took one very long sub (8200 seconds) to see how it all fared. I'll post it later when I get home from work, I haven't looked at it properly either yet :-)

[AndyUK]

... but the other night I took one very long sub (8200 seconds) to see how it all fared

Wow - That you have GOT to post! I've heard of (and seen results from) 3600s before, but that's an insane exposure (2hrs 20 mins) ! (I take it that wasn't a luminance then? )

[Tim]

If anything the focus may have changed a bit over the course of the exposure as it was taken between 2am and 4am when the temperature changes the most dramatically, but will have a look later

[JAS]

Does anyone know how deep the m48 thread can go before contacting the guide tube?

This could be exactly what I need, but I need to know if it will take the complete 6mm of male thread on my Skywatcher coma corrector.

Thanks

Jason.

[steppenwolf]

Does anyone know how deep the m48 thread can go before contacting the guide tube?

Unfortunately, it will only take 5.5mm so you are 0.5mm too deep and that doesn't allow any margin. You could use a 1.0mm Delrin spacer to buy yourself sufficient latitude.

[JAS]

Thanks Steve,

I think I can get an extra 1mm in there, just!

Jason.

[Tim]

Or use a 0.5mm delrin spacer There's a mix in the bag.

[Tim]

Here's the result of an image that I left to run for 8200 seconds the other morning. There was some wispy high cloud, and as expected the focus has changed a little during the exposure, but I am reassured that the OAG is solid and very unlikely to show any effects of flexure over the course of a normal duration exposure. Actually the whole assembly of imaging camera and OAG and guide camera now feels like one piece of equipment.

Cheers

IC1396 - Skywatcher Esprit 150, Atik 460ex, Baader 7nm Ha filter, OAG & Lodestar. No calibration frames, this is just as it came off the camera with a basic stretch in Nebulosity and saved as jpg.

[Zakalwe]

Lovely image Tim!

2hour exposure??? With my LP that image would be nothing more than a sea of orange

I finally got mine to come to focus, after much faffing about. I have yet to test it under the stars, but have achieved focus on but the imaging camera and guide camera (QHY5 mono). It was a LOT of messing about to get focus on both cameras and to get the orientation of the guide and imaging camera correct.

For anyone with a similar setup, then this is how Ive set mine up.

Setup: Atik 428, new Skywatcher OAG, Xagyl filterwheel,TRF-2008 reducer.

The stem of the OGG has to be pushed through the mounting turret so it protrudes into the camera. The top of the stem to the turret is 5.3mm.

I used a 3mm T thread extension sourced from Teleskop Express.

The camera is mounted with the male-to-male T-thread adapter thats supplied with the camera.

I used a Baader M48-to-T-thread adapter. This screws into the OAG and takes up no space.

To get the guide camera into the correct orientation I had to cut 2 x spacers from the cover of a Red & Black notebook. Each spacer is 0.66mm thick. These spacers mean that the TRF is screwed as far into the OAG as possible without hitting the prism stem.

The spacing is now 45mm from TRF to camera body. Allowing 13mm to the chip surface gives me a spacing of 58mm. Assuming that the filters (Baader) adds about 1mm to the back focus, then I am pretty much bang on the TRF specifications (56mm +- 4mm).

Looking down the business end I think that it should catch the light nicely and not obstruct the imaging chip (forgive the fingerprints everywhere!)

[Tim]

It always seems to be a lot of playing about with things when you first set up an OAG, but once you have the hang of it it is much faster than a separate scope, and a lote more accurate.

Looking at your second pic you should be fine like that shadow wise, but you could move the stalk up another 3 or 4mm by the look of it?

[Zakalwe]

It always seems to be a lot of playing about with things when you first set up an OAG, but once you have the hang of it it is much faster than a separate scope, and a lote more accurate.

Looking at your second pic you should be fine like that shadow wise, but you could move the stalk up another 3 or 4mm by the look of it?

Thanks Tim. Yes, there's a bit of latitude in the stem positioning. Thats as low as it can go without vignetting the daylight image. I'm not sure how steep the light cone is (f5) after the TRF, so I've stuck it as low as possible.

It's cloudy out tonight (typical) so I'll not get a chance to test it all tonight.

[Zakalwe]

Tonight was my first chance to test the new OAG. The conditions aren't brilliant at all...plenty of hazy high clouds kicking about.

I'm running some 15 minute Ha subs on the Iris nebula.

It seems to be doing the job nicely.

I also ran some subs through CCD Inspector...looks like the TRF is working nicely too (though would assume that I would get a flat field on the small chip in my 428Ex?)

[Zakalwe]

One thing that I'v noticed is that the camera image is riddled with stripes across the image. I never had these with the finderguider. I wonder if taking a PHD dark would help, or it a case of playing with the fain setting?

[Earl]

i always used to take darks with phd