FR spacing on a 618 chip

[Ewan]

Can anyone confirm the total distance from the glass in a 2" FR nearest to the DMK to the actual sensor to be 55mm ?

Or from the front of the FR nearest the Quark ?

Maybe a slight correction in distance will illuminate my images a tad better.

Thanks for reading

[Ewan]

From the DMK sensor to the first glass in the FR (rear) I have approx. 36mm, to the end glass (front) I have 55.19mm, this any good ?

[DrRobin]

Hi,

Moving the FR further away from the sensor will increase the focal reduction and you might be over-doing it for your Quark.  I had the same problem a couple of years ago, I needed less than 0.5x reduction, so cut down an Imaging Source nose piece (I had a couple of spares).  The stock nose piece is threaded all the way down and mine ended up around 5mm long.  This was enough to give me around 0.8x reduction and is now seeing some action again with an ASI174MM and a Quark.

As you get a C/CS adapter, you can use this to adjust the distance a little bit if you want more reduction.

Robin

[Ewan]

Hi,

Moving the FR further away from the sensor will increase the focal reduction and you might be over-doing it for your Quark.  I had the same problem a couple of years ago, I needed less than 0.5x reduction, so cut down an Imaging Source nose piece (I had a couple of spares).  The stock nose piece is threaded all the way down and mine ended up around 5mm long.  This was enough to give me around 0.8x reduction and is now seeing some action again with an ASI174MM and a Quark.

As you get a C/CS adapter, you can use this to adjust the distance a little bit if you want more reduction.

Robin

Hmmm 0.8 is not much of a reduction though I feel so I hope it doesn't come to that.

Without a spacer :-

With a 10mm spacer :-

I think I will need to experiment a little more to find what is best, using a 2" FR over the 1.25" shouldn't be an issue & should if anything give better illumination.

I will try it without any FR as well just to make sure.

I must admit sometimes I find trying to get an even flat frame is difficult, I seem to have tad darker corners top right & bottom left.

How does this image look to you Robin ?

[DrRobin]

Looks very good to me Ewan. I can't obviously see any dark corners, but viewing on an iPad isn't always the best. Thinking about it with a DMK21 even with 0.5x FR you are not going to get vignetting, not on a Quark. I don't with an ASI174, but do if I put a focal reducer on, but then it is 16:9 aspect ratio unlike the 4:3 of the DMK and I just crop the frame in the horizontal.

If you are getting dark corners in only two corners, especially if they are opposite, it is more likely to be the sweet spot of the Quark, unless something is out of line, then it might be two or three adjacent corners.

My first Quark had a bright patch in one corner and I know a few people have reported this. My present Quark has a slight unevenness across the frame, but it is more like a pattern of clouds. It is fairly in distinct until you push down the Gamma and a flat takes care of it.

Robin