M27 image with Coma using c9.25

[michael8554]

Hi Merlin,

Now you've confused me ( not difficult to do)

Is the Celestron manual saying the correct spacing is 95mm not 105mm?

Michael

[Merlin66]

Michael,

Hmmm

The 45mm plus the standard 55mm ( T2 adaptor 11mm plus DSLR 44mm) gives only 100mm spacing.

You are semi-correct, I also thought the optimum spacing was around 105mm.......

(Need to double check the actual effective length of the visual back adaptor...45 vs 50mm)

See Meade Manual added to previous post

 

 

[Merlin66]

On an early CN post:

Quote"Directly from Celestron: "For the Celestron reducer with a focal length of 231mm working at f/6.3, the spacing is 105mm."

(https://www.cloudynights.com/topic/403747-focal-reducer-to-ccd-distance-issues/)

I think the only way of actually confirming is to carry out a plate solve on the image and record the actual focal length .......

[Merlin66]

OK - issue resolved - well at least the "standard" Celestron spacing....

My micrometer shows that the Celestron T thread adaptor is actually 50mm shoulder to shoulder.

This means that when connected to a standard T2 +DSLR the spacing would be 105mm.

Hope this helps..

[alacant]

Hi. I think you missed focus, that's all. If you could move the camera closer to the reducer that should cure the edges and corners too. HTH.

[michael8554]

Hi Merlin

I've got that piece of paper too.

Makes no mention of the spacing required.

Shows the "T-Adapter" and camera, and a shorter "Off-Axis Guider" and camera, and various diagonals and a CCD, all with different spacings, without any mention of the effect on images and observing.

So is spacing non-critical or not?

Michael

[Merlin66]

Michael,

To achieve the reduction x0,63 the spacing should be very close to 105mm

This is based on info from the supplier and matches the physical spacing achieved with the nominated spacers. It makes no comment on the optical effects seen in the images taken.

 

[Imd]

19 hours ago, michael8554 said:

In my opinion the image with the tape measure shows the spacing is only about 95mm.

The spacing is measured from the back of the reducer, at 30mm on the measure, to the focal plane mark on the dslr body. This mark is on the top of the dslr body, but the white index mark for the rotating dial is close, if not identical, at 125mm on the measure.

This means the spacing is only 95mm.

Michael

Thanks Michael, I raise this with FLO to see what they say about this.

[Imd]

I gave it another go last night after I spent some time with the PA. PA was out a bit out but I expect would normally get away with that level of error when using my 200p. I tried using sharpcap to get a really good PA but that might have to be another thread  because the laptop seem to have a significant delay in reflecting changes made after the bolt adjustments. However PS is now much better. I also think I had better look with focusing and the results to me appear to be rounder stars reaching more into the corners than shown previously. I'm inclined to agree with Blinky that the SCT is probably more sensitive to field rotation field when using a DLSR.

Ill also speak to FLO about the 105mm Back focus

However I'm much more pleased with this image. I think I'll add a focus mask to my shopping list too.

I just want to thank all those who have helped me by discussing this subject. I'm always amazed by the members willingness to support each other and the collective expertise available.

Here is last nights image another M27 to help compare with the previous image - single 5 min exposure using a modified Canon 1100D, CLS filter, guided with a finder guider, moon not quite risen. Hope you like it, I did

 

[des anderson]

That`s a fantastic image for a first try, well done . Des