Need advice from EM400 or Tak owners

Paul Haese · #1 08-01-2009, 11:13 AM

Hi all,

I have an EM400 that I am trying to tame with auto guiding. It tracks fine unguided and I have taken images up to 15 minutes with near perfect stars.

When guiding near the celestial equator I get elongated stars.

I use PHD to guide with. I have tried a variety of aggression setting and still even with 5% aggression get slightly elongated stars.

It could be differential flexure but I get nice tight stars when guiding on targets such as Eta Carina.

PHD calibrates fine.

I have tried upping the guide speed but have been told to down it to 0.5. I have tried it at 0.7 once but that did not seem to make much difference.

I use a side by side system by ADM with a Tak TSA102 and ED80 (guide scope). DMK guide camera, but I have just bought an Orion Starshoot autoguider.

What settings do other users have in a) their hand paddle b) guiding programs?

I am taking all sorts of info in and have not discounted anyone's thoughts so far. I want to get this sorted out as it is most frustrating.

I want to thank JohnG and Strongmanmike for their help so far to narrow down a few issues. However there are some chaps here who have EM400's or the NJP and I would like to hear their thoughts.

Thank you.

Dennis · #2 08-01-2009, 03:15 PM

Hi Paul

Other than what I wrote on the Tak Yahoo group, I use the following settings on my EM200 Temma II:

In CCDSoft when I am imaging at FL of 1200mm or more, I set the RA drive correction rate to 0.5 from the default of 1.0.
When imaging at 1000mm or less, I don’t adjust the RA drive correction rate, leaving at the default of 1.0.
When using a separate guide scope (WO 66mm), PHD and Orion Deep Space Star Shooter (original model from 4 years ago) I expose for guide stars in the range of 2 to 5 seconds.

When I first did this test some 12 months ago, it did seem to reduce the star elongation when imaging with the C9.25 at F6.3 which is around 1480mm.

Good luck with solving this – I can fully sympathise with how frustrating this must be.

Cheers

Dennis

Paul Haese · #3 08-01-2009, 05:18 PM

Thanks Dennis. I thought it might be you on the Yahoo group but was not certain.

Do you adjust the Dec rate at all too?

gbeal · #4 09-01-2009, 05:38 AM

Hi Paul,
can't help with actual settings, but wonder about trying a couple of things.
If you have access to either an off axis guider, or alternatively an SBIG (with the in-built guide chip), maybe that would rule out the differential flexure possibility.
Can you mount the guide-scope on top, rather than side by side. I don't like side by side to be honest, and in your case any weight saving (and I doubt this too) will not be an issue with a beast mount like the EM400.
Gary

Paul Haese · #5 09-01-2009, 08:31 AM

thanks Gary, that would be one way of sorting that out. I have thought maybe the side by side might be the culprit but I know of so many people doing good work with them, so think that is unlikely. Mind you I am putting it on my final check list. Now just to get hold of an Sbig. Hmmm, I know where there is one......

montewilson (Monte) · #6 09-01-2009, 10:10 AM

My EM-200 becomes a bit goofy and gives me higher than normal guiding numbers if there isn't an imbalance in the counterweight/OTA loads. If they are perfectly balanced it seems to have a bit of slack.

Dennis · #7 09-01-2009, 11:47 AM

Here is a link to the Astrophysics Backlash Adjustment instructions for their AP600 mount which looks like a carbon copy of the EM200. I recently followed these instructions (for the RA axis) whilst chasing down some auto guiding problems with my EM200, although I haven’t had the opportunity to perform a before and after test just yet.

Cheers

Dennis

JohnG (John) · #8 09-01-2009, 01:49 PM

Hi Paul

Found this on Cloudy Nights.....

http://www.cloudynights.com/ubbthrea...4/Main/2522134

Also....

http://www.bisque.com/help/theskyV6/...roubleshooting

Cheers

Paul Haese · #9 09-01-2009, 05:06 PM

Thanks guys, I will look into these a little more.

John, I have seen the first thread on CN, I took quite a lot of notice of this.

I do wonder though from the second link whether my power supply is producing a true 12 power supply. Hmmm perhaps something else to track down.

Thanks Dennis for the link on backlash. If I find that this is the issue the mount will be going back to Japan for adjustment. Pretty unlikely but it may be part of the problem.

Monte, I tried doing off setting the counter weight system, but this had no effect, so that does not seem to be the problem. Good suggestion though and thanks for thinking of this.

Once I get this narrowed down and I find the problem I will let everyone know, just so that someone else will not have to go through this again.

Dennis · #10 09-01-2009, 08:38 PM

Is the EM400 a dual 12/24V DC system like the EM200? If so, I’d try a 24V DC mains adapter – at least such a test may discount that factor as a potential contributor to your problem?

Cheers

Dennis

Paul Haese · #11 10-01-2009, 09:53 AM

Dennis, yep it is dual voltage. I might just get a 24v DC adapter. You got any ideas where I can get one? I have a 12v DC adapter now, but have not seen a 24 around.

Paul Haese · #12 15-01-2009, 11:26 AM

Sorry Dennis for the late reply.

The EM400 is dual voltage and this does not seem to be the problem.

I have been in contact with several other chaps here that have either the same mount of the NJP. Through their accummulated knowledge I think I have sorted the issue. Albeit that I will do the tests first. I will let everyone know the solution when I find it. Differential flexure combined with guide speed seems to be the real issue here. However, tests first and then I will know for sure.

Thanks so much all for the suggestions and for the help offered.

Paul Haese · #13 21-01-2009, 07:17 PM

After much thought and consultation with some of the leading imagers around Australia I have come to the conclusion that this problem is really differential flexure.
Examining images from 6 minutes, the stars are perfectly round. When I examine images at 10 minutes I notice that there is elongation to varying degrees depending on what angle the scope was pointing at. For example I note that images taken which the scope is around 40 degrees in elevation present stars which are quite round. While images that are taken near the meridian have very oval images.

The same can be said for images longer than 10 minutes and once again depending on where they are taken in the sky.

So now the hunt for the culprit begins. Any suggestions as to which component may have caused your system to act in this way will be greatly appreciated and noted for me to check. When I find the answer I will let you all know and do something on my website as a check list to help others in the future. I note on the web there is not much written on differential flexure and more info would be great.