Re: GTF-81 Questions
- --- In William-Optics@yahoogroups.com, "underdriven255" <underdriven255@...> wrote:
>I should have looked closer, as this is actually an Optec unit and therefore is available here in the US at a lower cost: $275 (from their price list).
I don't have a flattener to try.
Regarding the focusers, the DDG part is an electronic piece, and I have an original one on my 80FD which is a Crayford style. I think the newest R&P design, whether with DDG or without is a better design.
--- In William-Optics@yahoogroups.com, "underdriven255" <underdriven255@...> wrote:
> Hi Timm,
> > The GTF102 is a larger version of the 5 element design with the
> > built in field flattener. When I bought it, William advised me
> > that I would need a 1.25" diagonal for most eyepieces.
> I am familiar with GTF102--it's a bit too big for me, although it is an impressive unit. Looking at the focal length vs. the tube length, the GTF102 seems to have less backfocus than the GTF81, so I'm not surprised that a 2" diagonal isn't supported. It seems to be very oriented to AP...
> Have you tried any reducers with the GTF102? I'm just curious if you have found any that work well with the flat field of the GTF scopes...
> Thanks for the eyepiece info...
> > The new R&P design of the WO focuser is very nice.
> Well, this is something of an enigma to me since Ray has indicated his DDG focuser had to be replaced, and he was sent a non-DDG unit. I have also seen several WO scopes on eBay recently (listed as new) which also have non-DDG focusers. A GTF-81 from Agena would have a DDG focuser, and I'm not sure if I would be getting the best version of the focuser or not. I'm sure WO would take care of it in any case, but I don't like to have doubts when I buy something...
> Thanks, Keith
- Hi Timm,
I realize that the DDG is the digital readout part of the focuser, however I am trying to use that in order to differentiate between the original R&P model and the updated one. I read a post from England where an original R&P focuser needed to be replaced and now Ray has had the same issue--in his case he received a non-DDG replacement which he says is much improved. While it is certainly possible that a focuser with a DDG readout could also contain the "new & improved" hardware, it is worth noting that Ray was sent one without the DDG display. Not that he seems to care that the DDG aspect is missing (and I wouldn't either), it is still something he paid for. My guess is that whatever hardware improvements were done to the R&P mechanism caused the cost to go up, and ditching the DDG display was a way to offset that cost increase. Of course, that is just a guess on my part...
It's not that I don't appreciate the situation that these small companies are in--they order a production run of X units, and if there is an issue they are faced with a tough decision on how to fix it. They can upgrade all the scopes and lose money or they can send them out as is and issue replacement focusers when people complain. For visual use the original DDG unit is probably fine--it is only for AP that there is a problem. So I would do exactly what they are doing and ship scopes with the original focuser. But from my perspective I'm not thrilled to buy a telescope that I know will require a focuser swap right away. Yes, Ray got a replacement and I probably would as well if mine had the problem, but I have to take that on faith...
With a 2 inch diagonal and a 6mm eyepiece the focuser is extended about 15 mm .
With a 20 mm is about 20 mm.
When I use my SBIG ST8300 and QHY filter wheel I use a 2 inch extender and no diagonal.
The focuser is extended about 20 MM .
It will probably work without the extender but I like using the extender by force of habit.
With a DMK I use 2 inch extender with no diagonal. The focuser is extended about 50 mm with this camera.
I see a GT81 for sale at Agena.
This model comes with an external flattener which can probably be replaced with a reducer flattener if desired.
May be this model might work better if you want to lower the F number.
Maybe William can comment on this.
> I have used a 2 inch diagonal with eyepieces from 4mm to 20 mmInteresting. How far is the focuser extended when you use a camera? I would think it must be fairly far back if you have enough back focus to use a 2" diagonal...
> with no problem.
> I am used to making sure the distance from the flattener to imageYes, I tend to assume that using a reducer or extender is simple--like attaching a teleconverter to a DSLR. But in reality the spacing constraints seem to be pretty tight in order to achieve maximum performance...
> plane is a specified distance.