Pitch Black Skies

Received with thanks from @CraigT82

Is there not only one side that is mirrored?

Can you upload a picture of it?

I'm eyeballing this OTA. Has anyone got any experience or opinions on it? It comes with a modified Skywatcher Atlantic coma corrector that reduces the focal ratio to 3.45.

18 minutes ago, alacant said:

We need a shot without a filter to eliminate the same, although I doubt they're the cause

You're right, similar problem with my L-filter from a couple of weeks ago.

I have struggled a little bit with tilt in the past. I had put it down to the focuser.

Mirror clips are removed, using your silicone method.

Here's a single Sii sub from CCD Inspector if they can help shed a bit more light.

CCD Inspector Sii.fit

CCD Inspector Sii Curvature.fit

Actually Oiii doesn't look great either, but not half as bad as Sii.

The four corners of each filter:

Sii

Ha

Oiii

1 hour ago, alacant said:

So it's not the cc then;)

I hope not 😆

1 hour ago, alacant said:

Do you have an L frame without filter?

Good question. No I haven't. I do have an L-frame of M31 that a took a couple of weeks ago if it's any help?

Are you trying to see if it's on all of my filters?

I can't really see the astigmatism on the Ha and Oiii that I attached.

Thanks @alacant

Good spot, I could see this too but wasn't sure what it was. I was thinking star trailing at first glance but wasn't sure.

These are 3nm Antlia filters, SHO. The coma corrector is Skywatcher Aplanatic.

There wasn't any major changes between each filter change.

37 minutes ago, newbie alert said:

Just because you run a autofocus doesn't mean that it's in focus

Indeed, that's why I then did a manual focus.

I can see some radial distortion in the Ha and Oiii subs, suggesting that the coma corrector is too far from the sensor.

11 minutes ago, Antlia_filter said:

For IC1396, the SII signal is not rich compared to Ha and OIII

Thanks, that's what I suspected.

12 minutes ago, Elp said:

Are you to say the stars never became solid between both extremes of focus?

Correct

13 minutes ago, Elp said:

though much stronger than o3.

No, it was quite the opposite actually. As you can see from the attached files the Oiii was much stronger than the Sii, despite Sii being twice the length.

Has anyone came across this before?

My stars look hollow, almost like doughnuts.

My first assumption was that the focus was out so I re-ran the EAFs auto-focus feature, same result...

I then manually focused it and the tightest I could get them still left them hollow.

This was the first light of my 1.25'' Antlia 3nm Sii filter on a 294MM Pro and SW130P-DS.

The Ha and Oiii were fine.

Another thing I noticed is that the signal through the Sii filter was only about 10% of what I could achieve through the Oiii and Ha filters. Is that just because the target isn't rich in Sii?

The target was IC 1396 (Elephant's Trunk Nebula)

Light_IC1396_600.0s_Bin2_294MM_S_gain120_20220826-233812_0001.fit

For comparison, here is a Ha and Oiii sub, which are half the exposure length;

Light_IC1396_300.0s_Bin2_294MM_H_gain120_20220814-012109_-10.0C_0001.fit

Light_IC1396_300.0s_Bin2_294MM_O_gain120_20220824-234735_-10.0C_0001.fit

Great first pic 👍

Well done, that is a HUGE improvement over your first attempt imo 👏 

...still not better than mine though 😏

Thanks, yeah I was considering the bin1 mode I don't think it is the best solution. 

27 minutes ago, scotty38 said:

You can use the smaller 2.3um pixels.......

Will the image be less detailed using bin2?

I used the bin1 mode on M31 a couple of weeks ago. It's much slower to collect light (4 times I think), the full well capacity is much less, there's a reduction in dynamic range, and the file sizes are huge.

Can I get an opinion on this telescope please?

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p7085_TS-Optics-70-mm-f-5-Quadruplet-Flatfield-Apo-mit-3-Element-FPL53-Objektiv.html

The sampling rate comes in at 2.75"/pixel paired with the 294MM. Is that anything to worry about? Should I be trying to get closer to 1.5"/pixel? My guess is that I would need a larger telescope to resolve down to 1. 5"/pixel anyway.

How important is the sampling rate and what is a good general guideline to have?

The CCD tool recommends ~ 0.7-2"/pixel for good seeing. With that in mind, the FRA400 gives out 2.4"/pixel on the 294 in bin2.

In the unlocked bin1 mode it gives 1.2"/pixel. Problem is, the full well capacity is very low and file sizes will be huge in that mode. The sub exposure times would probably be painfully slow too.

Similar situation with TS Apo recommended. 

Hi, welcome to SGL 💫

Glad you got it sorted Simon. The belt mod is fine upgrade to the HEQ5. Clear Skies 🙂

43 minutes ago, Simon Pepper said:

So just to confirm this is the two little hex adjustments when the RA is rotated one under the power box? Just need to ease back a little? Thanks 

This is a useful follow along.

I'm looking around for an imaging refractor and can't decide. 

I'm using a mono camera, 294MM with LRGB,SHO.

Do I still need a triplet to avoid CA even though I will be focusing on each colour separately? My guess is that problems will arise when shooting L.

I want to image large targets such as m31, m42, Elephants trunk nebula, etc. I find my 130pds just a little too cropped in for these. Collimation is becoming a pain and I'm not sure if I'm really keen on the diffraction spikes anymore.

Currently I'm looking at WO 72GT, SW 72ED, SW 80ED. These are within my budget.

Thanks, 

Alan

1 hour ago, michael8554 said:

What size is your OTA, you didn't say ?

5'' reflector, I think A4 should do.

Some really good suggestions there, thanks guys.

I'm finding it a bit inconvenient waiting for either sunrise or sunset to start taking flats as the weather can be unpredictable. It would be great to do them indoors before of after my session. Can anyone recommend a cheap light pad that I could use for taking flats?