SCT Q's - focal reducers, etc

[Texy]

Hi folks,

as explained in another thread, I,ve just done a deal for an 8" LX50 EMC OTA that I plan to mount on my motorised EQ4 until funds allow an upgrade. It'll mainly be used for visual use, but I,d also like to have a go at using my toucam and/or nikon D80 on lunar/planetary objects. I see that it is usual to use a focal reducer with SCT's in order to get the complete target in the FOV. I,d like to get a focal reducer, but because funds are limited, I only plan on getting one for now. Taking the moon as an example, can anyone advise which one would I need, 0.3, 0.5 or 0.6 ?

Also, I assume that typically SCT's do not suffer with not enough in-focus travel when connecting camera's, or is that not the case?

I have a generic camera adapter and T-mount, is that all I'll need for the nikon? I guess once the OTA arrives I,ll be able to answer some of those Q's, but thought I'd ask those that have already gone through this process.

Cheers,

Texy

[Merlin66]

Texy,

A standard x0.63 reducer is a good starting point. You'll need spacers/ adaptor to give you around 110mm from the reducer to the CCD chip. The x0.33 reducers are next to hopeless for imaging anything larger than a webcam sized chip.

You'll have no problems with focus travel!

Ken

[brantuk]

Yup - the .63 is what I use, with an adapter/spacer for the chip. It all works fine on my SCT with the Nextimage webcam

[Texy]

Cheers folks, and advance apologies for the clouds this weekend ;-)

Texy

[SteveP]

Hi Texy

Yes, a focal reducer is a great addition to an SCT both for increasing the FoV and also for reducing exposure times. I'd recommend a .63x. It's very versatile and they come up 2nd hand on a regular basis. If possible, look out for a Celestron. The only other thing you'll have to consider is to get the chip on your DSLR positioned correctly. As Merlin says, it needs to be 110mm from the rear of the reducer so you'll need to work out what size adapter you need.

The design OF SCTs where the primary mirror moves is great in that there is always sufficient focuser travel unlike some other designs.

Steve

[Texy]

Thanks - I think the 'standard' camera adapter I have is around 4 inches long, so in the right ball park figure. Interesting though, the 110mm figure quoted - is it the same for all SCT's, or just the Meade 8" ?

Texy

[brianb]

is it the same for all SCT's

Yes but not for all reducers.

[SteveP]

Texy

It's nothing at all to do with the scope itself. It's determined by the reducer's design. The Celestron .63x reducer (and I think also the Meade equivalent) bring the image to focus at 110mm behind the reducer and avoiding any vignetting. Other designs eg Optec's, have a slightly different focal point. Any particular focusing characteristics of the scope occur in front of the reducer

Steve

[Texy]

OK - understood.

Thanks.

[Texy]

I see that the celestron reducer is around £150, but the meade is only around £100. Is the celestron that much better? In any case I,d go for 2nd hand, where prices range from £50-odd upwards to £65, for either make.

Texy

[Merlin66]

AFAIK they are identical... just the rebadging.

A good clean s/hand unit would be the way to go.

Ken

[Texy]

Well I secured a japanese celestron F6.3 reducer for £60....from the same chap I got the LX50 OTA from as it happens.

Result!

Texy

[brantuk]

Good result and great saving