2" focal reducer works with DSLR?

[Kaptain Klevtsov]

Scopes N Skies are offering an Antares focal reducer in a 2" size, anybody know if it will work with a DSLR with the APS size chip? I've tried the 1.25" one and the vignetting is severe, maybe the bigger one is better?

TIA

Captain Chaos

[russ]

Hi CC,

Had my eye on that too. I presume it was designed with the larger chips in mind. A 0.5 reduction would be good. I wonder if it works with all scope types or whether it works better in only certain types...ie SCT/MCT?

Russ

[Kaptain Klevtsov]

Just ordered one to find out, I'll keep you guys posted.

Captain Chaos

[Ambermile]

Hi CC,

Had my eye on that too. I presume it was designed with the larger chips in mind. A 0.5 reduction would be good. I wonder if it works with all scope types or whether it works better in only certain types...ie SCT/MCT?

Russ

... why would that mak a difference Russ?

Arthur

[GordonCopestake]

The fittings might be different but as long as you can phyically attach it to your scope (ie it doens't have SCT threads if your using it on a 'frac) then it should work fine..... maybe

[russ]

Just wondered whether my Newt would have the focus travel to work with a reducer. Although these screw into the nosepiece, so it's not like the Celestron f6.3 which will absolutely not work.

Arthur, you think it will be okay? Be great to reduce the Newt from 1200mm to 600mm!

Russ

[Kaptain Klevtsov]

The fittings might be different but as long as you can phyically attach it to your scope (ie it doens't have SCT threads if your using it on a 'frac) then it should work fine..... maybe

Is that a definite maybe Gordon?

The bit I have ordered has the 2" EP thread and screws onto the EP or camera nosepiece. I'm getting a 2" nosepiece as well to see if I can get more of the light on the chip.

The issue is with the level of vignetting. I already have the 1.25" version and it just plain doesn't work. When I get it to focus with the DSLR (not an issue with the Skelescope) the lit up bit is much less than half the frame. As I already get vignetting with the 1.25" nosepiece I'm assuming that I'm seeing a wider field of the vignetting effect. Maybe the bigger nosepiece and FR will give me enough of the chip for it to be useful.

With the Skywatcher 200mm Newt. I can't see it working at all. This is because the 2" adapter is so long, and this adds another couple of inches to the serious lack of in focus travel that is needed.

I've managed to screw the 1.25" FR in the wrong end of the nosepiece but not tried it to see if I can get focus yet. This should reduce the FR effect by having the FR closer to the chip, but as it is the wrong way round, I have no idea if it will work with the camera.

I'm hoping that it lands before the weekend so that I can give it a go and report the findings.

Captain Chaos

[Ambermile]

Just wondered whether my Newt would have the focus travel to work with a reducer. Although these screw into the nosepiece, so it's not like the Celestron f6.3 which will absolutely not work.

Arthur, you think it will be okay? Be great to reduce the Newt from 1200mm to 600mm!

Russ

It will either work or it won't Russ, the scope shouldn't make a difference. You are interested in the *other* side of the reducer, not the scope side.

Unless you buy a reducer specifically designed for dslr's and their BIG chips you are pretty much always going to get vignetting or coma or some other sort of abberation.

Arthur

[Kaptain Klevtsov]

OK so it landed today. My questions about vignetting and focus across the chip are somewhat answered so I thought a follow up might help others.

As its not dark and it is cloudy, the targets were a tree and a car headlight.

The tree was my first target, this shows the level of dropoff towards the edges of the frame - not very significant I think, it seems less than I get with a 1.25" nosepiece and that can be processed out.

And a car headlight which has detail in the centre and at the edge.

There seems to be a little softening at the edges but nothing really serious. The target will usually be in the centre of the frame so the edges are just for framing.

Just to be complete here, I used the frac. for the quick test and it wouldn't wind in far enough to reach focus at infinity. 50 or 60 metres was the limit. I'm guessing that the Skywatcher Newt. has no chance at all, but the Skelescope will have no problems at all. Won't fit the other two as they take 1.25" EPs.

Might help somebody make a decision,

Captain Chaos

[GordonCopestake]

looks pretty good cc, thanks for sharing. nice images too.

[Kaptain Klevtsov]

On the same subject:-

I've tried getting this thing to work with the DSLR on the Skelescope but couldn't find focus or even close. It's definitely not through a lack of travel. The FR works on the thread of a 2" EP fine, so could I parfocalise the camera and EP without the FR, then add the FR to the EP, refocus, swap to the camera + FR and be somewhere near? I'm guessing that the distance from the FR to the focal plane of the camera and whatever the equivalent is with the EP would have to be the same for this to work.

Anybody good at sums?

Captain Chaos

[GordonCopestake]

I'de be tempted to get somewhere close and then move the camera back away from the focuser to see if it's back focus you need. If not then slide your focuser closer to the primary with your sled and then do the same thing until you find the right point. I regularly move eyepieces out of my diagonal to find focus rather than move the focuser for the DSLR if that makes sense.

[Kaptain Klevtsov]

I've tried the "somewhere close" idea, but I've no idea where that is. The D50 uses a carp mirror system instead of a pentaprism so that the viewfinder is 75% as bright as it should be and that doesn't help. If the focussing gets more critical with lower f/ numbers as it does with a camera, I could be going straight past it in both directions and missing the zone.

I'm also wondering about how much of the light cone misses the secondary if I slide the sled too close to the primary. ( I try to do the sled focusing with the R&P focuser about 5mm out from fully in to use the mirror as much as possible to keep the effect down). This would lose light that should be getting to the camera.

With the FR on an EP I was expecting lots of dim things to show up with a 40mm EP such as veils and north american things, but nothing doing. However I'm probably mistaken in that assumption.

Still fighting the clouds here so I don't get much chance to play with the setup. Next non-drizzly day I'm going to try a daylight test if i can get the Skelescope to aim at anything more than 500m away. My observing area is now shuttered and damp proof sheeted and looks like a paddling pool. Waiting for the concrete fairy to come.

Captain Chaos

[GordonCopestake]

Sounds like fun CC, you'll have to take lots of photos of your slab construction. Im thinking about a hard standing area myself.

As for focusing I think you'll have more luck in the day as you can see the whole field of view rather than a small object like a star or planet. I see what you mean about the sled being too close and the light cone hmmmmm. I'm still hunting an eyepiece thats parfocal with my DSLR. I need to do some testing. I wouldn't mind if i have to use a ring as long as i can focus an eyepiece and then swap the DSLR in and it still be in focus (or at least close)

Have you got a window to look through? Even that would allow you to try......

[Amith]

Hi Kaptain Klevtsov, I am looking to get a focal reducer for my SCT 6SE to be precise but I was told the threads on the t-adapter a different to that on the 2" focal reducer. I cant see your pictures unfortunately but would you mind telling me how you got yours together. The FR I am looking to get is the GSO 2". Thank you in advance for your help. Kind Regards, Amith

[kirkster501]

I use a 2" Skywatcher reducer with my DSLR just fine.