Clarkey

You need to add your scope to the telescope settings in Stellarium. From memory, from there it is quite simple although I am using a EQDIR cable not USB.

Ok, I understand now. I used to get the same problem. A plastic storage crate with the laptop inside was my solution, then a long cable into the warm, now a remote fanless PC which generates plenty of heat.

Why not use a dew heater? Alternately a quick blast with a cool hair drier is probably better than a heater. However, for planetary imaging it is probably less of an issue.

If your anything like me you will never be completely happy. I regularly go back and reprocess images that are just 'wrong' somehow. APOCD - a new SGL acronym 😆

7 minutes ago, FrenchyArnaud said:

Well, mostly because it does not. The focal length defines... the focal length

As I said above I probably needed to clarify my original query. Such as for the same sensor size.

9 minutes ago, vlaiv said:

That one is also easy to solve. If we look at geometrical optics - then combination of the lens can usually be replaced with single lens.

Yes, I understand this from the other explanations and I appreciate the differences. It would be a lot cheaper though😀

Thanks for the guidance. From the multitude of different answers I don't think I made myself too clear but I think I now get it. In effect, there is one primary ray that is effectively straight and not refracted. All the other light needs to be aligned to the same focal plane.

Just to add to my confusion, cameras have a fixed distance to the focal plane but can have any focal length lens. You could have one scope with multiple lenses😁

I think if I had drawn a diagram my query would make more sense, but I'm on holiday and using my phone.

19 minutes ago, M40 said:

Hopefully a couple of calculations will help explain...

Field of view (Degrees) = field of view of the eyepiece/magnification

Magnification = focal length of the telescope/focal length of the eyepiece.

Hopefully that will put you out of your misery, but if all I have done is muddy the waters further, I will be equally pleased

I understand these bits but it does not answer my initial question regarding WHY the focal length defines the FOV. At least the water is no muddier🤣

There are really lots of options, much of it down to personal choice. I'm sure the FRA300 is ok, I have no personal experience. I would maybe consider the FRA400, which is a similar design but you can get a reducer to give F3.9 at just under 300mm FL. Maybe more flexible? There are other similar scopes and I would not worry about using a flattener or reducer.

As for the mount I can't really comment. I have an heq5 which is about the minimum you want for a 'proper' scope. I think the AVX is similar. Maybe a used neq6 or similar might be a good option?

For the camera I would seriously consider mono. The initial outlay is more, but it gives more flexibility and improves light polluted photography. I thought I would not really use narrowband when I brought my kit, but now the bulk of my widefield imaging is NB. Also helps with the moon. 

The ASIAIR is a fair choice but does limit you to ZWO products. I use a mini fanless PC to run my set up so I was not tied to one company. Yes it needs a fair bit of set up, but gives you the choice of other kit. (I have a risingcam imx571 for the cost of a 183.

Autofocuser is fine. I use senso Sesto just because the are neater and easier to install. But with the ASIAIR.....

Power - probably go bigger than you 'need'. Nothing worse than running out of juice.

Finally, get a couple of good books before diving in. Mistakes are costly! 

I will warn you, if you get hooked it is a slippery slope to poverty 😆

I have been pondering a though which I am sure has a very simple answer. However, my old and naddled brain is not coming up with the answer. (Physics was never my strong point).

Why does focal length dictate the FOV of a scope? For example, a simple refractor of a given focal length will show a certain amount of sky. Why could you not alter the lens shape to focus the same area of sky at a different point? Same with a mirror system.

Any guidance to put me out of my misery would be appreciated. (Be aware, I do have a penchant to miss the glaringly obvious 😀).

I have used stellarium without issue. If the mount starts in the home position it is normally approximately right for the first slew. I think the alignment positions are held in EQMOD when synched. As more stars are synched it gets more accurate (normally). Maybe the data is not clearing from EQMOD? Do you shut your PC / Stellarium down between uses?

I would check, but I think this may be what you are looking for.

https://www.firstlightoptics.com/skywatcher-focusers/astro-essentials-2-dual-speed-low-profile-crayford-focuser-for-newtonian-telescopes.html

I think the hacksaw option is the 'standard' route.

55 minutes ago, Paul2019 said:

I'm loving pixinsight. 

Not something I can agree with. I have PI, but I find it like playing pass-the-parcel with boxing gloves on😁

I assume your camera is not modified. This would really help picking up the Ha signal. But if you have good stars at 300s that's good.

I would not bother with darks with the 200d as it will probably add more noise than it removes, especially with 4.

Not sure I would try threading anything made out of cheese.

I would agree. Adjust your back focus until at least one corner is right. After that it is probably tilt. Looking at the image, I think if you get it close enough you probably won't notice any tilt unless you pixel peep.

I had just started a reply. Beat me to it!

650nm is a very low cut off point. Not only loosing Ha and SII but half the red spectrum. Strange for an astrocam?!

45 minutes ago, poogle said:

Also, will I need an IR/UV filter at the same time as my narrowband filters?

No. The IR/UV wavelengths are removed by the NB filters. You only need this for normal OSC imaging.

9 hours ago, SuburbanMak said:

couldn't really leave one of the kids behind..

I think you need to check your priorities 🤣

1 minute ago, Anthonyexmouth said:

not being able to afford to eat

Look on the bright side - you can save the money by turning off your heating while you are outside imaging in the winter. Every cloud....😁

5 minutes ago, Anthonyexmouth said:

My credit card is gonna hate me

Mine stopped talking to me years ago.🤣

6 minutes ago, Anthonyexmouth said:

sound like you approve

Definitely. Excellent scope for the money.

I got my SM 90mm just before new year (and the price increase). Although at this point I was largely using my longer FL scopes for galaxy imaging, I did use the SM a few times. In most areas I think it is excellent. It is well made with a focuser that works for AP - most of my other scopes have not been so good. The made-to-measure flattener reducer is also excellent. Optically it is also very good with no visible CA.

My only question with it is the cooling. I set it up along side my ED80 on my dual rig (first and only use so far) and the SM focus drifted way more than the ED80 which stayed pretty constant. As I put my scopes out in plenty of time, the only reason I can see for this is cooling of the optics being very slow. I will be trying it again soon with the new season starting so I can see if will always be a potential problem. If you are using it on its own with an auto-focuser I would not hesitate to get one (especially if you can get one of the ex-demo models cheap).

These images are using the SM90. The top one is LRGB plus Ha - something like 8 hours total integration using the F4.8 flattener. The second was a combination of ED80 with a Canon 600D plus Luminance with the SM90. The final image was the SM90 only at F6 using the SM flattener. I did not use any star reduction on these images so you can make your own decision on how 'good' the stars are. To be honest the processing was fairly minimal -as was the set up. On the last image the flattener probably needed to be moved out a fraction, but on the California nebula it was plug and play.

7 hours ago, PottyMonster said:

How I wish I could afford a ASI2600MC-PRO

Rising Cam IMX571. Pretty much the same camera but half the price. Slight gamble with warranty but much better value. There other manufacturers selling it under a different name at low prices too.

Back today!!! Yey!!!!😄😄😄

4 hours ago, Lee_P said:

There are lots of RC8 telescopes out there with different branding, but they're all basically the same, right?

As far as I know there is not much between them optically. Focusers and other bits might be slightly different, but as far as I'm aware pretty much the same.

My only question is regarding cool down time with carbon tubes. My 90mm Stella refractor is very slow to cool.

52 minutes ago, 900SL said:

I was thinking around 6 nm would balance cost/performance?

On your own there. I still have the ZWO filters. Astronomik and Antila seem to get good reviews. Depends on how deep your pockets are....