OAG Questions

[jnc71106]

Hello all

I've been think about getting an OAG lately but I have questions that hopefully can be answered here

I image with a atik 314, atik MFW, 0.8 reducer and I have a Lodestar guidecam

I've been looking at getting the TS OAG9. I've no doubt been reading far to much and have now confused myself

1/ Where should the OAG be placed in my train ? Before or after the reducer ?

2/ Is it correct that the distance from prism to guidecam chip should be the same as prism to imaging chip ?

3/ I've seen it mentioned that getting the cameras parfocal during the day is a good way to avoid a headache trying to do it at night. Does the daylight target need to be a certain distance away or doesn't it matter ?

4/ Does anyone use this combination of cams and OAG

5/ I know the lodestar is very sensitive and it's superb when using a guidescope but when using an OAG are there likely to be issues finding a guide star ?

Cheers no doubt I will have more questions

[Uranium235]

Firstly, do you actually need an OAG? If you havent got flex, it isnt broken and therefore you dont need to fix it.

I used to have the said OAG9, and if you get one youd better have a swear jar on standby. I have a similar setup to yours (bar the fancy APO), have you tried using a finderguider? Youre at 480mm so a similar solution (with proper mountings) should work just as well.

1) It should be set up as: Reducer > OAG > FW > Camera

2&3) Yes, it needs to be the same distance. This is the most difficult part of setting up and it will drive you bonkers, do it in daylight to save your sanity. Choose a target a couple of hundred feet away (chimney, tree etc..), it doesnt matter that much on distance though as the point is to get both cameras to focus at the same point.

4) Did, until I needed cash for an NEQ6

5) The first thing you will notice - unless you have a perfect prism (had to have one changed on mine) is that your stars dont look like stars, but thats where the fine tuning comes in, and it can be quite time-consuming to get it right. Also the prism needs to extend far enough into the light cone so as to get enough light, but not cast a shadow on the CCD chip. The best solution was to position it parallel to the longer edge of the CCD chip, then its much easier to know where the OAG is looking in relation to your camera.

[dmahon]

1) aAter the reducer (before the filterwheel)

2) Yes

3) In the distance is best. Remember the lodestar doesn't have to match exactly - slight out of focus can be better (bigger stars)

4) Probably. I use SX throughout - is there. Reason you aren't going with a matching Atik OAG?

5) No

See these reviews:

http://www.firstlightoptics.com/user/atik-efw2-filter-wheel-oag-review.pdf

http://www.firstlightoptics.com/user/starlight-xpress-filter-wheel-review.pdf

[jnc71106]

Thanks for answers. Gives me something to think about

The atik OAG adds to much to the distance between the 314 and reducer

[ncjunk]

The TS will give you strange star shapes be it still guides ok. I understand there is a certain trade of in poor star shapes due to its thinness.

At focal lengths of 600mm you wont find too many areas where guide stars are difficult to find but there are a couple where i end up guiding on poor stars.

on the C11 at 1800mm then its a pain finding guide stars in areas away from the milkyway. M27, for instance, isn't a problem as there are loads around there.

[Merlin66]

If you can source suitable adaptors and provide the space , there's no technical reason why you couldn't position the OAG before the reducer.

[Explorer 190 MN]

Dunno if you got your answer, started reading all the posts and got bored..

I used a Atik 314L+ TS OAG9mm and a lodestar guide camera.

As the TS OAG 9mm was built with DSLR in mind the distance from the telescope side of the OTA to the imaging chip should be 44mm ish.

Here is a picture of my setup

I am planing on shortening the bit the holds the prism on 10mm so I can screw the adjustable extension in a bit and maybe ditch the hotec compression fitting to gain another 20mm to get my CCD closer the the recommended 133mm from the back flange to the focal plane but thats another story to be investigated with CCD inspector. The Monorail focuser put me at 175mm but because the Atik CCD chip is only 11.2mm diagonal I am not sure the 133mm really applies to me and the recommended distance is for fixed extension lengths and an adjustable focuser.

Time will tell

[jnc71106]

Thanks for all your help on this everyone that answered. I might give it a try just to see how I get on. If one comes up s/h I will definitely go for it as there is nothing to lose really, if I don't get on with it I will just sell it back on

Cheers