Mount without guiding for scope with short focal length (say <200 mm) and 3-5 min sub

[Erquy]

Hi,

I am looking for a mount for telescope/lens of focal length say below 200 mm without need of guiding and for say 3-5 min exposure if possible keeping 100% subs -so to say reliable and not just luck to have a "good copy". if this is too demanding focal leng down to 130mm, yet> 100 mm would still be interesting above 3 min (reliably again). My pixel size if 3,7 to 4,5.

This would mean a resolution of 4.7 "/pixel or higher, so it shall accept long sub even with a periodic error which could be smooth enough over 8-10 min period and p2p of 8-10 ".

would there be anything out there doing the job?

Note:

- it does not need to be a compact small mount type (Adventurer type, which I understand would not manage in most cases), as above set up with short FL would be occasional (I also have a WOGT81 and C8 which would be used guided in such cases), yet something one could transport easily

- I believe the key is a mount with a smooth long period.

For example: Belt driven (e.g. avalon Evo Zero? Or what about the new harmonic mount type AM5 and the like? Those are to be guided, but I wonder if really needed for FL 200 or below for few min. 

 

The reasons behind:

-convenience, so to avoid having to guide (no oag nor guiding scope/additional camera to handle) 

- replacement of the AVX (very happy with it, I do manage up to  3-5 min unguided at 180 mm keeping most sub (75%), it has only  a 1-2 very steep minutes in its PE, the rest is good to give <5" over 3-4 min), but It is now getting rusty after 10 years -it stays outside- and when I use it guided, its backlash is just a pain (e.g. forget automatic meridian flip, I am running it also east heavy + slightly misspolar aligned so I guide in 1 direction -in such way I do manage RMS of 0.8-1.2 which is I think pretty good -I have not use the PPREC in phd2 yet, but I think it shall work good on RA as I have a well reproducible PE). So hopefully there are mount out there today that can do better today?

 

Alternatively: would any have a suggestion for a compact guide scope (I have asi 224 mc I could use)?

 

thank for some idea!

Edited May 9, 2023 by Erquy

[Elp]

SVbony 30mm guidescope will do. There's a zwo one which looks very much the same but the former is much cheaper.

[Elp]

Why do your subs have to be so long? Make them shorter and take more of them to reduce risk of throwing any away. There may be noise differences but it's a lot easier to work this way.

 

[Erquy]

Elp, thanks. 

Longer is only a matter of convenience, faster overall processing and less storage space (especially from canon raw files which is my main intention for such set up/short focal). I run up to 5-10 hrs total exposure, so it matters, especially with my laptop when I am out at our summer house over several nights or somewhere on vacation and without a stationary computer (and no patience to wait going back home to process the data on stationary). I have been running out of space several time on the laptop (during processing with pixinisght, I need to delete intermediate files after the debayered, cosmetized, alignment etc... before the whole processing is completed). Alternative would be a new higher end laptop, or external disk which is of course feasible (yet still slow also to process due to very large amount of files). My current laptop is an old lenovo (U330p, i5, 8GB ram)

example below is 8,5 hr on Iris with FMA180, Canon raw with avx 4 min exposure sub, non guided. 126 files of 30 MB to start with, so already 3,4 GB.... (which "explodes" into several 10´s GB when processing those into all intermediate files of pixinisght and  I only have some 40 GB availale unfortunately). With 2 min, I would not be able to process this on the laptop and it would take ages...

I would prefer investing in a new mount than a new laptop (apart the space limitation and a bit slow on big job, the lenovo serves me extremly well -must be about 8 years old and spent many night down below -15 to -20 and it has never let me down!)

[Elp]

Understandable. If your usb ports are and run at full usb3 speed you can use a usb SSD drive, I've got a similar issue and sometimes pre process straight from the external SSD. Or just back everything onto a usb HDD and process when you need to.

[Erquy]

good point, checking up, it looks my old lenovo has 1 3.0 USD... just need to figure out which one!

[ONIKKINEN]

Reading your situation it still sounds to me like the overwhelmingly easiest and cheapest option would still be to just set up guiding. Any 30mm guide scope, mini-pc ziptied/velcroed somewhere on the setup (need not be fancy) and you are set. Any guiding will be better than no guiding at all, no matter what you might think about the backlash of your AVX.

On 09/05/2023 at 23:59, Erquy said:

- replacement of the AVX (very happy with it, I do manage up to  3-5 min unguided at 180 mm keeping most sub (75%), it has only  a 1-2 very steep minutes in its PE, the rest is good to give <5" over 3-4 min), but It is now getting rusty after 10 years -it stays outside- and when I use it guided, its backlash is just a pain (e.g. forget automatic meridian flip, I am running it also east heavy + slightly misspolar aligned so I guide in 1 direction -in such way I do manage RMS of 0.8-1.2 which is I think pretty good -I have not use the PPREC in phd2 yet, but I think it shall work good on RA as I have a well reproducible PE). So hopefully there are mount out there today that can do better today?

So without guiding you are rejecting 25% of all subs and its still acceptable? Sounds way too much for normal operation to me. Scrapping 25% each night would be a disaster in my books.

Like you said you have 5'' error in every sub and you find that acceptable, but guiding results in up to 1.2'' error so to me it seems obvious that you should just keep guiding as its 4x better? Who cares about backlash if the end result is 1.2'' RMS at a resolution of 4.7''/px, that is excellent guiding for the setup.

On the last part, if there are mounts that can do better than yours (yours sounds like a really good copy of a mount). There are mounts with encoders, but these are very pricey: https://www.teleskop-express.de/shop/product_info.php/info/p12834_iOptron-GEM28EC-with-iPolar--Case-and-LiteRoc-Tripod.html

Again, by far the simplest and most cost effective option is to just guide.

[SamAndrew]

I would get one of the smaller ioptron mounts with an RA encoder, that should keep the RA axis well within the requirements. The periodic error on the AM5 would be too great for your desired sub length.

[900SL]

Different useage for me, but I use a Fornax LT2 unguided when travelling, greatly simplifies everything and I get excellent guiding with a good polar alignment (critical if unguided)

No go to, you have to reframe after every 90 mins or so, but 3 minute subs at 250mm no issue, also excellent for wide angle. The whole set up easily fits in a small backpack