My focal plane is inclined, please tell me how to fix it? Thank you!

Hi everyone,

I'm from Shanghai, China, I'm an amateur astronomical observer. Early this year, I purchased a used STT-8300 from the United States, because I believe that the SBIG product is the best, so I excitedly began shooting. Soon, I found that photos cannot be entirely clear, so I started to adjust the various components of the telescope. I let the telescope Depot overhaul and re-customize the extended barrel, but not solve the problem. The CCDInspector software analyzes photos flatness as the following diagram:


I also customized the focal plane adjustment ring. I found that the focal plane adjustment ring need a very substantial adjustment can restore the photo to normal, please look at the following picture:


I also connected through a telescope CAA rotating the extended barrel and STT-8300 to different rotation angles, and took photos, I found that the situation did not change, indicating that the optical axis of the telescope's probably no problem. You can download the photos taken in different rotation angles from: http://pan.baidu.com/s/1hq471C4 , in "STT-8300" directory.

So, I increasingly suspect that STT-8300 itself.

Last night, I connected a DSLR camera(Nikon D70S) in the back of the telescope, found the flatness of the pictures is basically acceptable, just like this:

I basically can determine STT-8300 CCD chip inclined. I have never opened the camera, it may be due to the negligence of production, or the seller may be improperly adjusted.

Now, although with the 'focal plane of the adjusting ring' can correct the tilt of the CCD, but this makes the CCD chip is not in the center of imaging plane , it may affect the image quality. So, I need your help, I hope you can give me some suggestions or methods on the adjustment of the CCD chip, the camera can fix my problem. My ability is good. If you have any suggestions or methods, please tell me, I may try to fix the problem myself. Because I was in Shanghai China, the cost of return the camera to the United States will be expensive, and there are risks during transport.

I love astronomical observations, I eagerly hope to get your help to improve my STT-8300, thanks!


All photos mentioned in this mail can be downloaded from http://pan.baidu.com/s/1hq471C4 , including the telescope and STT-8300 work photo, and the connection diagram.

Thank you very much!

Yang
2014/10/25

 

Dear Yang,

I looked into your case and you need to contact Bill in tech support.
Repairs: bill@sbig.com

Regards
Tim

 

Thank you, Tim!
I have sent a email to Bill, and waiting for his help.

 

Yes, me too. Here is how I fixed it:

I went to an autoparts company and bought some "shims" I was able to put one 10 mil under the side of the attachment of the camera to the scope. Tim has informed me that there are devices that will adjust the shim, BUT, there is a short backfocus to the STT 8300M and this becomes problematic with my Tak 180ED.

All this showed up for me when I collimated the 180 ED that has a critical focus depth of only 17 microns. I wasted 6 months trying to fix the scope when it was the CCD.

You would think with what we paid for these CCDs we would have flat chips. I had to put black electrical tape along the fix to keep the light out. Resale value with black tape?

The more I think about this the more irritated I get.

I ran all the same tests with my Nikon D800 and the collimation was perfect. Nikon chips are FLAT.

I am in a particularly irritated mood this am because last night at 4AM the STT crapped out, why, because of the power cable. There is also a chronic problem with unstable power connections and this unit. No fix is offered. the fix supposedly is to widen the opening of the internal connector (tiny slit in post), well this works for a day or two.

Just to show I am not completely negative about the CCD, I love the off axis guide chip, BUT....

 

PS, go out to my astrobin site and you'll see more CCDInspector shots:

http://www.astrobin.com/users/jerryyyyy/

Eventually I used PixInsight to get things quantified.

 

Hi jerryyyyy,

Your photos are beautiful! I hope in the future I can shoot the same beautiful photos.

I thought my problems STT-8300 is a case, it seems not. There is a problem needs to reflect, the power lines cracked after using a few times, I can only use a heat shrink tubing to reinforce, as shown below:


I hope SBIG attention to product quality and consistency.

My STT-8300 has been returned to the manufacturer to adjust, and hope to have better results.
Thanks to Tim and Bill!

Yang
2014/11/6

 

Thanks for the complements. I researched the STT 8300M a lot before I bought it. You might check out the pictures from Pfile out there. He uses a STT8300 also and is very experienced. You can search by equipment.

I could have used a larger chip with the Takahashi, but all the CCD cameras with the larger chips seem to be very old technology. I was one of the first to get it and went through a lot as an early adopter as the initial drivers did not work well. The camera is worth the price just to get the OAG/filter wheel engineering.

BUT, as you say the attention to detail in manufacturing is a problem. I cannot understand why they cannot get these chips flat. If you have the problem and I have the problem, others must too and just do not see it because they are using scopes with wider critical focusing depth. The formula I learned in microns is F*F*2.2 or for the Takahashi 180 ED 2.8*2.8*2.2... which is very small 17 microns, a hair starts at 40 microns. This was never a problem with my F10 C8... 220 microns wide. If you look at my photos using PixInsight on Astrobin, you will see there is a residual tilt that I have been afraid to try to fix. The shim fixed the X-axis but there is still a slight tilt in the Y. If I try to fix Y... what happens to X? Cannot shim in two directions. The Takahashi collimation is perfect. I verify this using my Nikon d800 whose chip is perfectly flat.... I also spent $600 sending the scope to Takahashi in Texas to verify this . They could not figure out the problem. I bought a Hotech laser and the manufacturer figured it out in 5 minutes by asking me to rotate the STT and the error rotated with the camera. It does not with the Nikon. I could try to improve things, but "the enemy of good is perfection."

I am very thankful for the picture of the power connector! I must have the same problem because they told me it was the CCD internal pin that has a little slit in it. I have fooled around with that a lot to no avail. I must also have the cable problem. I will look into the heat shrink tubing. Another fix might be superglue/epoxy at joint of the wire to connector, but I like what you did.

I purchase cheap electronics on AliExpress (China's Amazon) and their manufacturers make a big deal of how well they reinforce cablings for say an iPhone/iPad so that these problems do not arise.... these are $0.87 cables and better than what Apple makes due to the heavy reinforcement.... costs them nothing.

 

Just got my camera back and they said they checked the chip and it was OK. I have tons of rain here but supposed to be clear tomorrow and will test the collimation.

 

Well, I took my shim out and am measuring tonight and have the gradient back. The tilt stays constant when I rotate the camera... that is the tilt is In the camera. These are images with the tilt showing before rotation after and again back to the original rotation. You get the same gradient left to right. I recolimated in between.

My conclusion is you just cannot see this small tilt with your instruments.

This takes hours. I will have to put the shim back in tomorrow. Hopefully I can remember exactly how I did it.

BTW this is after the stock Tak focuser was replaced with a Moonlight one. They have a tilt adjustment, but if I use that, my Nikon D800 will be off.

 

Yes, here is the shim back in.

 

I had a cosmic insight today talking to a unnamed software developer.... he said that this could be the spacer. The spacer between the SBIG and the Tak was custom made by Precision Products. He suggested rotating the spacer and see if the problem rotates with the spacer. I hope the 4 screws are symetrically positioned....

 

Hehe these guys know me probably too well to be unnamed. I hope you can solve this one.

 

I found the drawings we used originally. The screws are symmetrically arranged. Not sure I have the courage to pull everything off and rotate to determine if it is the adapter. If I rotate the adapter for the camera to be tight it will also have to rotate to the same degree...

I talked with the gent at PreciseParts who is very familiar with my adapter and says I could measure the flange and he would be shocked if it cam up with a 10 mil error. I have to use a 10 mil shim. He agrees that rotating the part would be proof it is not his part.