Advice Required Choosing a Long Focal Length Scope

[Jkulin]

I have a good deal of experience with the iOptron CEM60EC it was the dogs danglies, loved it, I then had an opportunity to upgrade to the iOptron 120EC and that arrived on Saturday morning, so I am still setting everything up, @RayD and my mate have the 120EC so I had first hand experience of the mount of seeing my mates usage of it.

When the CEM60EC first came out, there were a good number of complications, iOptron worked hard to resolve them and in my mind there is absolutely nothing to touch it in it's price range now, I only upgraded not out of need but because a very attractive deal came my way to upgrade, I have no doubts there there will be a few hiccups, but if it gets to be as good as the 60 or it demonstrates the potential to be even better then it will be a keeper. I have been working to get everything installed and operational and it just amazes me with the features it has, truly a gorgeous looking mount.

https://www.ioptron.com/product-p/7301.htm

What really appeals to me is the High precision tracking with low periodic error (PE)<0.15 arcsec RMS

Mechanically it is sound, they are just about to release a new firmware which should fix the small amount of bugs remaining.

BTW I have a GSO/Altair 8" RC and a GSO 10" RC Truss and I'm very impressed with them, I also have an Esprit 80 and 100 and love using them as well, personally I love sharp long diffraction spikes, so I get the best of both worlds.

The CEM60EC handled the 10" superbly and Ian at Altair Astro will normally always do a deal, if you are going to the PAS this weekend, then check out my mates stand www.656imaging.co.uk, Peter has borrowed my mates 120EC and will also be showing off his AD250 DK which is fantastic, my other mate has one and it is just amazing. Peter's also just bringing out a range of Newtonian Astrographs at some amazing prices, so have a chat with him.

HTH.

[Chris Willocks]

I've been watching some reviews of the CEM120 and it looks very neat. It also looks easy to balance with the silky smooth drives. Apparently, this is one of the only complaints of the Mesu 200 i.e. that the friction drive makes it difficult to balance. I also like the cable management system of the CEM120. I think it would be useful, especially in an observatory setting.

[Jkulin]

Just fitted mine to the pier, it really is a beautiful piece of kit: -

It might not look it but that bar weighs nearly 10Kgs as does each of the weights, all of the controls are silky smooth as well.

[vlaiv]

2 minutes ago, Jkulin said:

Just fitted mine to the pier, it really is a beautiful piece of kit: -

It might not look it but that bar weighs nearly 10Kgs as does each of the weights, all of the controls are silky smooth as well.

Lovely!

Please tell me if housing is cast metal on these mounts or machined? For some reason, after HEQ5 and other synta parts (like focusers on achromatic scopes, ota rings, etc), I've developed disliking of cast metal parts for scopes. Machined metal looks and feels (maybe even performs) better.

[Jkulin]

I really don't know Vlaiv, all I can say is that everything fits together smoothly, the head unit weighs 23Kgs, but I can't really tell, sorry.

NB. The head has a crinkle finish which makes it difficult to determine any seams.

[DaveS]

Lovely piece of kit.

If funds don't stretch to a DDM 85 Basic (The other versions are a bit pricey) then I'll be looking at one of these, though using a DDM 60 has put me right off worm-and-wheel. The DDM mounts have NO periodic error or backlash. The software also has a utility to refine the balance after rough balancing, by measuring how much current it takes to move the axes in each direction. When the current is equal the axis is balanced.

DDM85

[vlaiv]

2 minutes ago, DaveS said:

Lovely piece of kit.

If funds don't stretch to a DDM 85 Basic (The other versions are a bit pricey) then I'll be looking at one of these, though using a DDM 60 has put me right off worm-and-wheel. The DDM mounts have NO periodic error or backlash. The software also has a utility to refine the balance after rough balancing, by measuring how much current it takes to move the axes in each direction. When the current is equal the axis is balanced.

DDM85

Omg look at that price tag

I'm sure it is however exceptional piece of kit.

[DaveS]

Yep, exceptional it it. Pricey, but comparable to a 10 Micron GM2000 HPS Monolith.

[bob-c]

Very nice John, I think you will be very pleased with it as well  as for the money mate.

 

Chris, I have one of these mounts ,had it since last October and it is a great piece of kit.. I am in the same position as you now, as far as what LFL scope 

to put on it. Will be having a good look around at the PAS on Saturday.

[Chris Willocks]

Once again, I appreciate all the feedback everyone. In my mind, I think it will be between the Mesu 200 and CEM120EC2. They are both around the same price point.

I think I will give the SX AO a miss, as I'm not confident enough to spend that much money on something that I might get frustrated with.

Also, I think I'm pretty set on the Esprit 150 as well. It seems to have a decent reputation and I like the fact that it is easy maintenance as @swag72 says.

In terms of camera to suit it, I'm really leaning towards either the Atik ONE 9.0, SX Trius SX-814 Mono or possibly even the QSI 690. Not sure which would be the best?

I just came across this image gallery below in which a similar setup is used i.e. Esprit 150, Trius SX-814 and a GM1000HPS.

The images are very impressive.

 

[alan4908]

1 hour ago, Chris Willocks said:

Once again, I appreciate all the feedback everyone. In my mind, I think it will be between the Mesu 200 and CEM120EC2. They are both around the same price point.

I think I will give the SX AO a miss, as I'm not confident enough to spend that much money on something that I might get frustrated with.

Also, I think I'm pretty set on the Esprit 150 as well. It seems to have a decent reputation and I like the fact that it is easy maintenance as @swag72 says.

In terms of camera to suit it, I'm really leaning towards either the Atik ONE 9.0, SX Trius SX-814 Mono or possibly even the QSI 690. Not sure which would be the best?

I just came across this image gallery below in which a similar setup is used i.e. Esprit 150, Trius SX-814 and a GM1000HPS.

The images are very impressive.

Hi Chris

I was alerted to your post by your link to my image gallery  - if you are interested to getting close to DSO's then I've found that around 0.7 arc seconds/pixel is about optimum for my site in the UK. As you mentioned, I current image using an Esprit 150 in conjunction with a SX-814 (which gives you 0.7 arc seconds/pixel) and a GM1000HPS mount.  I'd definitely recommend the Esprit 150 - it is an amazing scope for the price.  In terms of your choice of camera, I'd suggest you give consideration to the resulting resolution that your various camera options would yield- I've been very happy with my SX -814 which has worked flawlessly. 

On the mount front, I made the move to 10micron since I wanted to improve my imaging efficiency,  since we have so few clear nights in the UK. My reasoning was that if I could image unguided then I wouldn't loose any sub frames due to a guide star fading due to a passing cloud, all that would happen is that the resultant subframe would have a signal to noise degradation.  The amount of degradation would obviously vary from hardly noticeable to significant, so I'd simply discard the poor ones and keep the good ones.  Given the UK weather, I've found this approach to imaging has really boosted my output.  

Alan

[vlaiv]

3 hours ago, alan4908 said:

Hi Chris

I was alerted to your post by your link to my image gallery  - if you are interested to getting close to DSO's then I've found that around 0.7 arc seconds/pixel is about optimum for my site in the UK. As you mentioned, I current image using an Esprit 150 in conjunction with a SX-814 (which gives you 0.7 arc seconds/pixel) and a GM1000HPS mount.  I'd definitely recommend the Esprit 150 - it is an amazing scope for the price.  In terms of your choice of camera, I'd suggest you give consideration to the resulting resolution that your various camera options would yield- I've been very happy with my SX -814 which has worked flawlessly. 

On the mount front, I made the move to 10micron since I wanted to improve my imaging efficiency,  since we have so few clear nights in the UK. My reasoning was that if I could image unguided then I wouldn't loose any sub frames due to a guide star fading due to a passing cloud, all that would happen is that the resultant subframe would have a signal to noise degradation.  The amount of degradation would obviously vary from hardly noticeable to significant, so I'd simply discard the poor ones and keep the good ones.  Given the UK weather, I've found this approach to imaging has really boosted my output.  

Alan

We talk a lot about theoretical resolution and sample rate and you seem to be very satisfied by 0.7"/pixel. I think we have genuine opportunity here to put theory to the test.

Would you be willing to "donate" some of your data for this purpose? All that is needed would be linear stack of lum sampled to 0.7"/pixel. It does not have to be full image, crop is fine, just select section with decent SNR and detail that you feel justifies 0.7"/pixel. Just make sure data is linear, "fresh out of stacking" and post it as 32bit fits.

My intention is to take that image segment, bin it 2x2 (not regular bin, but one that I developed - I'll explain how it works) and then resample it to original resolution (effectively doubling it back to original size). Then we can examine difference of these two images and see if there is loss in detail and by how much.

What do you think about that? Would you be willing to try this?

[alan4908]

5 hours ago, vlaiv said:

We talk a lot about theoretical resolution and sample rate and you seem to be very satisfied by 0.7"/pixel. I think we have genuine opportunity here to put theory to the test.

Would you be willing to "donate" some of your data for this purpose? All that is needed would be linear stack of lum sampled to 0.7"/pixel. It does not have to be full image, crop is fine, just select section with decent SNR and detail that you feel justifies 0.7"/pixel. Just make sure data is linear, "fresh out of stacking" and post it as 32bit fits.

My intention is to take that image segment, bin it 2x2 (not regular bin, but one that I developed - I'll explain how it works) and then resample it to original resolution (effectively doubling it back to original size). Then we can examine difference of these two images and see if there is loss in detail and by how much.

What do you think about that? Would you be willing to try this?

Hi Vlaiv 

Sure !

Here's  a crop of a FITS stack of Lum stacked data of a recent M51. I've limited the image to a small crop of the central region core and converted it to a FITs file. I'd be interested to understand the effect of binning on deconvolution since I've found this to be a powerful process for recovering maximum detail. Please note that this it has been stacked in Pixinsight so everything has been normalized between 0 and 1. 

Alan

 Mean L M51 core.fit

[hughgilhespie]

Hi Chris,

One point to keep in mind with your Pulsar observatory is that it is much better to go for a 'piggyback' arrangement of scopes, rather than side by side. The shutter opening is fairly narrow, I think about 600 mm, and with a side by side arrangement, when you allow for the lack of accuracy in the dome rotation position, say +/- 50 mm, there is a risk that one of the scopes will be pointing at plastic, not the night sky. 

HTH.

Regards, Hugh

[vlaiv]

Here are results of lower sampling resolution of the data @alan4908 provided for this test.

First a bit about methodology and what should one expect to see from data loss. For comparison purposes I created "baseline" that shows what happens when resolution is lost. I did this by taking original data and applying Gaussian blur with sigma of 0.4 (very slight blur). Then I subtracted two images to show difference between them, and this is result:

Left on the image is linear stretch of difference between two images - original and blurred and right is histogram to show distribution of error. It loosely follows gaussian distribution with standard deviation of ~0.0001. More important thing is to look at difference image - it clearly shows structure of high frequency components of spiral arms of galaxy. As this is difference between original and blurred version - it clearly shows that blurred version is missing detail.

Next I used supplied data to do 2x2 bin on it. I did not use standard bin method, but rather "sift bin" algorithm (that name is just something I made up ) - that works as follows: it splits image into four sub images - each image gets "every other pixel" (all combinations of odd and even indices). These subs are aligned by using 3Lanczos interpolation and averaged. Here is result:

Next step was to use small 2x2 binned image and resize/scale it back to original size. This step is something that I'm not fully satisfied as I don't have scaling implemented with 3Lanczos interpolation and had to rely on Cubic O-MOMS from TransformJ package (ImageJ plugin). However I believe difference to 3Lanczos to be minimal.

Here are original and resized bin 2x2 side by side:

Above are stretched linearly, here is non linear stretch in Gimp:

Left is original, right one is simulated 1.4"/pixel sampling. To my eye there is slight difference between the two evident in bright stars and somewhat in structure.

In order to quantify difference between the two comparable to our baseline, I've created a difference between original data and 1.4"/pixel one:

I find the result very interesting. It's immediately obvious that no clear structure is present in comparison to base line and much more noise difference is seen. Noise can be explained by higher SNR of binned version - so it's obvious that original will be noisier and noise in difference comes from that. It's not so obvious where is lost detail. If you look at statistics you will notice the difference between base line and this - baseline has standard deviation of error at 0.0001 while binned one has stddev of 0.0005. It turns out that gain in SNR is higher than loss in detail when resampling to 1.4"/pixel.

Only thing that I find objectionable to above is fact that stars look a bit distorted in resized version. I'm not sure if this is consequence of using Cubic resampling algorithm instead of 3Lanczos for upscaling or just fact that stars in sample data are very tight and deviate from Gaussian profile (closer to Moffat for example).

[Chris Willocks]

15 hours ago, alan4908 said:

Hi Chris

I was alerted to your post by your link to my image gallery  - if you are interested to getting close to DSO's then I've found that around 0.7 arc seconds/pixel is about optimum for my site in the UK. As you mentioned, I current image using an Esprit 150 in conjunction with a SX-814 (which gives you 0.7 arc seconds/pixel) and a GM1000HPS mount.  I'd definitely recommend the Esprit 150 - it is an amazing scope for the price.  In terms of your choice of camera, I'd suggest you give consideration to the resulting resolution that your various camera options would yield- I've been very happy with my SX -814 which has worked flawlessly. 

On the mount front, I made the move to 10micron since I wanted to improve my imaging efficiency,  since we have so few clear nights in the UK. My reasoning was that if I could image unguided then I wouldn't loose any sub frames due to a guide star fading due to a passing cloud, all that would happen is that the resultant subframe would have a signal to noise degradation.  The amount of degradation would obviously vary from hardly noticeable to significant, so I'd simply discard the poor ones and keep the good ones.  Given the UK weather, I've found this approach to imaging has really boosted my output.  

Alan

Hi Alan, thanks for the information and feedback. It has definitely given me more confidence regarding which scope and camera to go for.

Do you use a flattener on your Esprit?

 

5 hours ago, hughgilhespie said:

Hi Chris,

One point to keep in mind with your Pulsar observatory is that it is much better to go for a 'piggyback' arrangement of scopes, rather than side by side. The shutter opening is fairly narrow, I think about 600 mm, and with a side by side arrangement, when you allow for the lack of accuracy in the dome rotation position, say +/- 50 mm, there is a risk that one of the scopes will be pointing at plastic, not the night sky. 

HTH.

Regards, Hugh

Hi Hugh, thanks for the recommendation. The shutter width was one my main concerns with the Pulsar domes. That's why I will probably go for the larger 2.7m model, which has the larger 700mm wide shutter. I just think it is more futureproof, should I ever decide get to a larger scope etc.

 

Thanks,

Chris

[alan4908]

2 hours ago, Chris Willocks said:

Hi Alan, thanks for the information and feedback. It has definitely given me more confidence regarding which scope and camera to go for.

Do you use a flattener on your Esprit?

Hi Chris

Yes, I do use a flatterer on the Esprit, it is the one dedicated to the scope- see here https://www.firstlightoptics.com/esprit-professional-refractors/skywatcher-field-flattener-for-esprit-150.html

Alan

[Chris Willocks]

Thanks Alan, I was also looking at this TS Optics flattener, as it seems to have slightly more backfocus: https://www.teleskop-express.de/shop/product_info.php/language/en/info/p10307_TS-Optics-PHOTOLINE-2--1-0x-Flattener-fuer-Refraktoren-und-Apos.html.

I presume this would be compatible with the Esprit 150.

Chris

[alan4908]

1 hour ago, Chris Willocks said:

Thanks Alan, I was also looking at this TS Optics flattener, as it seems to have slightly more backfocus: https://www.teleskop-express.de/shop/product_info.php/language/en/info/p10307_TS-Optics-PHOTOLINE-2--1-0x-Flattener-fuer-Refraktoren-und-Apos.html.

I presume this would be compatible with the Esprit 150.

Chris

Hi Chris

Personally, I wouldn't make that assumption.  I'd have thought that flatteners would have to be matched to the relevant scope if you wish to achieve an optimally flat field.

Perhaps @steppenwolf could comment (a fellow Esprit 150 owner) ?

Alan

[steppenwolf]

1 hour ago, Chris Willocks said:

I presume this would be compatible with the Esprit 150.

I don't know how good this TS flattener would be with the Esprit 150 but what I can tell you is that the 150 and its dedicated flattener have given me the flattest field I have ever found in an imaging system! I'm with Alan on this one, I wouldn't take the chance when there is a proven solution available - thanks for alerting me to this thread, @alan4908