FLT98 and Reducer/Flatenner

[evansg]

Hello,

Anyone using the William Optics FLT98 combined with TRF-2008 (0.8 Reducer/Flatenner)?

I have just purchaced TRF2008 in order to use it on my FLT98 and ATIK383L+

I 'm just checking the perfect distance (from reducer end to ccd chip). I cannot get in any way perfect results counting 50-54mm. (My best attempt was on ~ 40mm having a little coma on left side.)

I would be grateful if anyone share his knowlegde to that

Thanks a lot,

Vangelis Souglakos

[gbealnz]

Hi Vangelis,

Not using the FLT, but certainly have used the TRF2008 on a variety of refractors, more laterly the GT-81, and suggest about 56mm from chip to rear of the reducer, it works for me.

Are you measuring from the chip, or front surface of the camera?

Gary

[evansg]

Hi Gary,

I am measuring from the chip! It is still weird

The best distance for my FLT98 is 41 - 42 mm

I will do more tests tonight...

[BlueAstra]

I use the TRF-2008 x0.8 with a Meade 5000 ED80. The recommended distance is 56mm +/- 4mm, for use with telescopes focal lengths 400-600mm. My setup with an SX(OAG+FW) + SX-H16 puts the CCD at 60mm.

[evansg]

Hmm, Using my Starlight filter wheel and TS-OAG9 i can count 52mm distance. Unfortunately stars at the edges are not ok. Too much coma.

What about the edged stars of your Meade ed80 (using the reducer)?

[BlueAstra]

This is an example shot from earlier in the year. Stars look reasonable in the corners.

[BlueAstra]

That shot was a narrowband Ha, so perhaps not a fair test of the reducer. This one is in LRGB, and apart from some mis-registration of the RGB looks OK in the corners.

[evansg]

Indeed, they look very nice!

Maybe i'm doing something wrong. I will check again tonight..

[BlueAstra]

Is the coma symmetric? If not you could have tilt in the system if the components are not perfectly flat against each other. Also try a spacer to increase the working distance (or try not screwing the FR all the way in, use a thick piece of card or plastic as a washer).

[gbealnz]

It was a pointed answer I admit, I wondered if you are including the front surface of the camera to chip distance, which is "normally" about 15 - 20mm. Didn't want to be rude and make it sound like you didn't know what you are doing, LOL.

I have reducer/SX OAG/TS filter drawer/H-16 (or M25c) as my optical train, using the W/O GT-81, or other refractors.

Post a picture of your focuser/reducer setup and let's see what you have.

Gary

[evansg]

Good morning,

Coma is symmetric so it seem to be no tilt. I have allready some spacers (1mm) and i have bought a variable T2 extender. So i have tried a lot of distances (the better approach was on 41mm).

Gary, i have calculated the extra distance in the ccd chamber. I think it is 10mm extra BUT i 'm not sure that the ccd chip is exactly there (behind the BK glass).

I will post a picture of my camera setup (oag, filter wheel, reducer, atik383l+) to be sure

Thanks for your help

[evansg]

I have done a better measurement and here are the results:

From ATIK 383L+ to T Thread = 17mm *

* I had mistakenly calculated a shorten distance

SX filter wheel = 29mm

TS-OAG9 = 9mm

+- 2mm on connections and spacers.

Adding all these: 57mm

Unfortunately the optimal distance for the FLT98 is 51mm.. so i have to remove my OAG and find another way to guide

Reducer has done his job. Calculating the F/L on MaximDL using PinPoint Astrometry, I got the following results:

Pos Angle +112° 00' ®, FL 498.5 mm, 2.23"/Pixel

Thanks everybody for your help

[pilkinn]

I've just recently got a FLT98 and was wondering about which flattener to use. The Televue TRF2008 says it's for 400-600mm focal lengths and as my FLT98 is 618mm I decided against it.

[gbealnz]

Pilkin. Give it a go, if you can borrow one that is, I have used mine on a 612mm refractor, and this week plan on using or at least trying it on a new 102/650mm refractor. Worth trying anyway.

Evansg. So, this is what I was trying to polity say, and maybe it was right. Maybe try the reducer at the correct distance and see if it works or not, then work out how to incorporate it. In my case I ended up "thinning down" the OAG a bit, mind you the TSOAG9 is as thin as you can get most likely.

Gary

[evansg]

Pilkin. Give it a go, if you can borrow one that is, I have used mine on a 612mm refractor, and this week plan on using or at least trying it on a new 102/650mm refractor. Worth trying anyway.

Evansg. So, this is what I was trying to polity say, and maybe it was right. Maybe try the reducer at the correct distance and see if it works or not, then work out how to incorporate it. In my case I ended up "thinning down" the OAG a bit, mind you the TSOAG9 is as thin as you can get most likely.

Gary

Yep, Gary you were right