My Atik 314 v's 460 thoughts

[swag72]

I have recently purchased an Atik 460 after using the 314L+ for about a year. I think in that time I got a fairly good grounding in CCD's and learning how to use them.

Getting the 460 was a big decision as I wanted a wider field of view on my Pentax 75SDHF, so I really ummed and ahhed over the 460 or the 4000. Sensitivity won through in the end for me.

In using the 460, there are a couple of surprises for me so I decided to post here incase there is any interest!!

First of all, my methods my not be the most scientific, but I have tried to keep everything the same and just changing over the camera's.

Each image has been taken with the following.

• Pentax 75SDHF
  
• Baader 7nm Ha filter
  

314 v's 460 direct comparison

Here are 2 images, of IC405. Each one is 1200s and the only change is the camera. The images have not been cropped at all and have both had a 'medium' preset stretch in Maxim. These are single subs.

I am surprised by a couple of things.

1) The masses of stars on the 460 image compared to the 314. I know that the fov is much smaller with the 314, but the nebula is almost lost in the stars.

2) The apparent lack of nebula detail in the 460 image compared to the 314. I suppose this can be explained by the different field of view and if they were both scaled to the same size that may not be as apparent.

460 20 minute sub v's 10 minute sub

After seeing the above 20 minute sub, I began to wonder if perhaps the 460 is so sensitive as to not require such long exposures and perhaps that would cut out some of the stars. So below is a comparison of one 10 minute sub and one 20 minute sub - I was interested to see how much detail would be lost.

I don't think that I've lost very much detail between the subs.

My thoughts on the 460 so far are a little mixed, let me explain.

1) The download speed compared to the 314L+ is very slow which I am finding annoying for framing.

2) The sensitivity when I am framing just isn't there and I am having to use 30s at 3x bin sometimes to even see anything. Very unlike the 314L+.

To be honest this last reason was why I thought that the 460 was much less sensitive than the 314, but when looking at the comparisons above, perhaps not.

As I said, just a few musings. Please feel free to join in and give me your thoughts on the images - Perhaps I am barking up the wrong tree altogether.

[jnc71106]

very interesting Sara. no idea what to make of it all will be interesting too see what others think.

[swag72]

I look forward to some more thoughts on this as I am definitely not feeling the love with this camera at the moment.

[jnc71106]

lets hope its just teething issues with the camera, perhaps its a little of expecting a leap in performance but because the 314 and 460 are similar in sensitivity your not seeing much of a difference

if that makes sense, it did in my head when i was writing it

the 30s loop for framing is a bit of a suprise. i know i can get an image for framing with 10s on 2x2 bin with my 314

[pete_l]

Thanks for that report, it's exactly the sort of thing I love reading on the forum: direct comparisons between pieces of equipment - keep 'em coming!.

So far as the cameras are concerned, the difference in QE is 65% (314+) vs. 77% but the 314+ has pixels that are twice the size of the 460's 6.45microns vs. 4.54 = 40 sq-microns to 20 sq-u. So the '460 is 20% more efficient at collecting photons, but each pixel only sees half as many - given the scope doesn't change.

It's not unreasonable that the '460 takes longer to download, it has 4x as many pixels - though I can see why it's annoying.

Have you got an raw subs that you're willing to share?

[ Later ] Thinks .... your issues with framing - presumably that's framing through the Ha filter, is it?

[AndyUK]

Hi Sara,

The slow(er) download speed is sort of understandable as the file size is 4x greater (ish), but the need to go to 30s @ 3x3 seems pretty extreme to me, especially as from what I've read elsewhere the 694 chip is supposed to be more sensitive than the 285, not less... . However, maybe if you set a subframe roughly 1/4 the size of the full 460 frame (to replicate that of the 314L+) it might show the same with roughly the same download speed(?).

I'd be very interested to hear the thoughts of other 460 owners though, as it does seem a bit bemusing...

[davew]

Pete could have a point. I wasn't aware there was such a difference in pixel size, not being familiar with either chip.

How long does a sub take to download ? There are cameras that take over 20 seconds to download. I hope it's not that bad.

Dave.

[swag72]

Sub download speed is probably between 5-7 seconds at max. Not a deal breaker, but compared to the 314, it's mighty different.

Still wondering about anyone elses thoughts on what I should be experiencing with this. Ive got some pretty awful artifacts after processing as well ....... This just isn't working for me.

[Gina]

As I recall, there's lots of people using the 460.

[swag72]

You're right Gina, but at the moment I'm not too pleased with it!.

Here's another quick comparison.

2 images - The 314 image is on the right in both cases, but I have looked at one star and on the 314 the Maxim readout shows about 22k ADU whereas the 460 is showing 65535 - Is it as simple then as I am over exposing the 460 and it doesn't help to have a 20 minute sub.

314 Maxim readout

460 Maxim readout

[RAC]

Very interesting. I would love to see a 383 in the same test.

[Martin-Devon]

Sara, I have also recently transitioned from a Atik 314L+ up to the Atik 460EX and I seem to have had a very different experience to you. For the framing with the 460, I shoot in Lum only and 2xbin - I take 1 second subs and they download almost instantly. If I want to do narrowband, once I have the frame roughly where I want it with Lum I switch to H-alpha, refocus, and do a 20 second 2xbin - I usually see loads of detail & it confirms I've got the target in the frame OK. I then switch to 3 second continuous sub downloads in H-alpha 2x bin to optimize the frame and camera angle - then do a 1 min sub to check that it's really as I want it - usually is, or just some very minor fine tuning, then I run my series of 10 min subs. I've never had any issues with picking up bags of nebulosity - you've probably seen my image of NGC7000 in the deepsky section at the moment, all in H-alpha (this and others with the 460 are also on my Flickr link). Also, I've not had any artefacts with the processing, but I never had these either with the 314 so I cannot really shed any light on the issues you're having there. If you're not happy with the 460, I expect that the dealer you purchased from would be perfectly happy to switch it to a 4000. I have quite a different set-up to you and don't know how much this may influence drawing comparisons with your experience. Hope you get settled soon one way or the other though since I know you debated long & hard on the choice of the CCD - good luck!

[Gina]

Sorry you're not pleased with your 460 Sara Especially with the amount they cost!

[Whirlwind]

Hi Sara

Just as a question but were these imaged on the same evening? What's interesting to note is that the minimums (background) on the 460 is running at a level of 21887 compared to the 314 of around 1491. To be honest if you were imaging in halpha onyl i'd expect the figure to be nearer the 1500 figure. With a a figure of 21887, you've 'lost' almost a third of your well depth to background 'pollution'. Because you have a low well depth in the first place with the 460 you are losing a lot of potential in your image (basically your dynamic range is being reduced as well as low level signal is being lost into the background noise). Therefore compared to 314 I'd expect the 460 to have lost the ability to show more signal as shown in your top image.

I can't understand though why using a halpha filter you should get such a high minimum though - the background signal looks like what i'd expect from being in a high light pollution area with a Luminosity filter.

As such i'd check the following:-

The filter wheel is working correctly with the 460 and it is actually selecting the halpha filter (or that you haven't chosen the wrong filter - I've done that!)

If you were imaging the targets on different nights that the moon wasn't almost on top of the target when using the 460

That you haven't got any light leaks into the system

Also have you taken any dark frames at the same temperature - if you have what are the minimums? This should narrow down a chip or imaging issue.

Have you applied any calibration frames (or is the software doing it automatically)?

Can you post a single fits file somewhere so we can see the artifacts as it's difficult to judge on the compressed images what might be going on?

Ian

[swag72]

Hi Ian,

To answer your questions I hope .......

No these were imaged on different nights. I don't know about the moon on the 314 image, but it was not far from full moon on the 460 image - Perhaps that can account for the high background ADU figure. I was really surprised at that when I looked at the subs and it was probably that figure that started my alarm bells ringing.

Here's a few fits files.

IC405 314 - https://www.dropbox.com/s/77aeivu60mcu3ez/IC405-314L-Ha.fit

IC405 460 - https://www.dropbox.com/s/ewisi5p53ricnxo/IC405-460-Ha.fit

IC405 460 600s sub - https://www.dropbox.com/s/oz2gxuif0vne12e/ngc1499_600s.fit

IC405 460 1200s sub - https://www.dropbox.com/s/aebigiw3ffvheka/ngc1499-1200s.fit

I am absolutely 100% certain that I had the Ha filter selected and also that there is no light ingress.

I have no darks as I was hoping to avoid them as I always did with the 314L - Never used a dark. The artifacts that I have would appear to be a bias artifact, as I restacked with no calibration files and it was fine. So back to the drawing board with that as well.

[Whirlwind]

Hi Sara

I've had a look through your images. There's nothing wrong with the NGC 1499 ones, just don't think you've pushed the 1200 one enough to show the difference. Ive had a bit of a play with them, the 1200 (on the right) definately has more data and you can work it harder. Also the background on both of these is nearer to what i would expect.

With regards the 460 IC405 image, something just isn't stacking up, I'm afraid.

The full moon would explain higher background levels, however still these are surprisingly high given that you are using 7nm ccd ha filter. I would not expect to have seen such a high minimum with such a filter and so many dimmer saturated stars compared to the 314L.

Looking at NGC1499 the dimmer stars aren't saturated either nor does it have a such a high background levels. And as they were only taken a day apart moon brightness levels should have been similar (not exactly admittedly and the image was taken a few hours earlier).

As such I really can only come to the conclusion for the IC405 460 image only the wrong filter was accidently selected which was rectified the following night.

Not sure about what the artifacts you spoke of though are? There seems to be some tracking errors/flexure causing eggy stars, but it's hardly noticeable and not really worrying about when you are testing a new set up.

Thanks

Ian

[JacobvonChorus]

I just did a quick process of the IC405 data to compare and I agree that something isn't right. It could easily have just been some mistake made. I would suggest retrying it to see if you get different results. If the same problem arises consistently then there really could be a problem. The California Nebula looks just fine though, I was able to pull quite a bit out of it (very similar to Whirlwind so I didn't post it).

Jacob

[swag72]

Thanks very much for that Ian and Jacob.

I can only think that I really did have the wrong filter selected for IC405, although I would stake my life on it not being the case!! I will go back and try IC405, double check the filter and let you know!