cheap f4 reflector: am I crazy?

[laser_jock99]

1 hour ago, alacant said:

Almost forgot. Secondary collimation: you have to get the primary donut on the Cheshire cross-hairs. Why do guides recommend having the tube horizontal? It's impossible to do like that. With the tube pointed vertically, the secondary adjusters behave in a totally predictable manner and it takes just a few seconds. At any other angle, you're up against gravity pulling against the secondary and it becomes a frustrating mess. Of course, you must have tool-less adjusters. HTH.

Ideally you should collimate the scope when it's pointing in the direction you are shooting in- especially if you haven't done the spring upgrades. A good laser collimator helps here as it should only take a minute or so to fine tune 'on the fly'.

[alacant]

18 hours ago, laser_jock99 said:

Ideally you should collimate the scope when it's pointing in the direction you are shooting in

Phew, yeah. The thing being if you're doing more than one target; the camera has to removed to put in the Cheshire. Then I've no way of re-orientating the camera for flat frames the next day. ATM, all I check in between is focus. So far I've been lucky. In 4 sessions the collimation has barely changed. Here is what it does with more exposure and the t2 coupling to the mpcc. Beginner's luck? Has to be.

 

[laser_jock99]

2 hours ago, alacant said:

Phew, yeah. The thing being if you're doing more than one target; the camera has to removed to put in the Cheshire. Then I've no way of re-orientating the camera for flat frames the next day. ATM, all I check in between is focus. So far I've been lucky. In 4 sessions the collimation has barely changed. Here is what it does with more exposure and the t2 coupling to the mpcc. Beginner's luck? Has to be.

 

Nice image. If your temperature is fairly constant over the course of the night you might get away with one collimation/focus. From past experience I think it's good pratice to re-check both before a extended imaging run especially if you have slewed the scope a lot to a different part of the sky.

Flats- I always try and keep the camera oriented in one position in the focuser. Thus I can use a 'master flat'  for most situatuations.

My master flat (hugely stretched for SGL purposes) for 8" F4 Newt with Baader MPCC III

[Astrosurf]

On 28/01/2017 at 21:44, alacant said:

Almost forgot. Secondary collimation: you have to get the primary donut on the Cheshire cross-hairs. Why do guides recommend having the tube horizontal? It's impossible to do like that. With the tube pointed vertically, the secondary adjusters behave in a totally predictable manner and it takes just a few seconds. At any other angle, you're up against gravity pulling against the secondary and it becomes a frustrating mess. Of course, you must have tool-less adjusters. HTH.

For those who collimate with screw drivers and Allen keys, you keep the scope horizontal in case you drop the tools onto the mirror. Not nice!

Alexxx

[Astrosurf]

On 28/01/2017 at 21:44, alacant said:

Almost forgot. Secondary collimation: you have to get the primary donut on the Cheshire cross-hairs. Why do guides recommend having the tube horizontal? It's impossible to do like that. With the tube pointed vertically, the secondary adjusters behave in a totally predictable manner and it takes just a few seconds. At any other angle, you're up against gravity pulling against the secondary and it becomes a frustrating mess. Of course, you must have tool-less adjusters. HTH.

EDIT: duplicate post

[alacant]

Progress report.

I did laser_jock99's compression spring and fat dovetail modifications. Of course now I don't know which has made the biggest difference, save to say that the collimation checks as near as dammit each time. It may have the reputation of impossible-to-collimate-Cheap-Chinese-Rubbish, but it takes great snaps.

I had a chance to try a skywatcher coma corrector -which plate solves to 730mm- giving a wider field and f3.5. Unless there's a bright star in the fov, I think it gives a better image than my Baader. The focus is really tricky with the swcc though (faster ratio?);  a cracked Bahtinov mask doesn't help either and so I think I missed dead centre focus. Anyway, here's a snap with a Canon 700d:

[ollypenrice]

2 hours ago, alacant said:

Progress report.

I did laser_jock99's compression spring and fat dovetail modifications. Of course now I don't know which has made the biggest difference, save to say that the collimation checks as near as dammit each time. It may have the reputation of impossible-to-collimate-Cheap-Chinese-Rubbish, but it takes great snaps.

I had a chance to try a skywatcher coma corrector -which plate solves to 730mm- giving a wider field and f3.5. Unless there's a bright star in the fov, I think it gives a better image than my Baader. The focus is really tricky with the swcc though (faster ratio?);  a cracked Bahtinov mask doesn't help either and so I think I missed dead centre focus. Anyway, here's a snap with a Canon 700d:

Another good one.

Olly

[Adam J]

5 hours ago, alacant said:

Progress report.

I did laser_jock99's compression spring and fat dovetail modifications. Of course now I don't know which has made the biggest difference, save to say that the collimation checks as near as dammit each time. It may have the reputation of impossible-to-collimate-Cheap-Chinese-Rubbish, but it takes great snaps.

I had a chance to try a skywatcher coma corrector -which plate solves to 730mm- giving a wider field and f3.5. Unless there's a bright star in the fov, I think it gives a better image than my Baader. The focus is really tricky with the swcc though (faster ratio?);  a cracked Bahtinov mask doesn't help either and so I think I missed dead centre focus. Anyway, here's a snap with a Canon 700d:

Very nice, it would be good to get into the habit of including your exposure details though, its hard to gauge the absolute performance without knowing if this is 30mins of data or 48hours. Also this probably shows me to be a total noob but I don't recognise the target as its not one I have had a go at before. 

[AKB]

58 minutes ago, Adam J said:

but I don't recognise the target as its not one I have had a go at before. 

NGC 2174, Monkey Head nebula, I believe. 

 

[alacant]

1 hour ago, Adam J said:

exposure details

Hi. Yes, bad habits. I know and so assume that so does everyone else! It's around 50 minutes. 

38 minutes ago, AKB said:

And again. Thanks. Confirmed as 2174 -or 2175- in Orion.

[laser_jock99]

7 hours ago, alacant said:

Progress report.

I did laser_jock99's compression spring and fat dovetail modifications. Of course now I don't know which has made the biggest difference, save to say that the collimation checks as near as dammit each time. It may have the reputation of impossible-to-collimate-Cheap-Chinese-Rubbish, but it takes great snaps.

I had a chance to try a skywatcher coma corrector -which plate solves to 730mm- giving a wider field and f3.5. Unless there's a bright star in the fov, I think it gives a better image than my Baader. The focus is really tricky with the swcc though (faster ratio?);  a cracked Bahtinov mask doesn't help either and so I think I missed dead centre focus. Anyway, here's a snap with a Canon 700d:

Nice image- good to see the modifications have made the scope more stable. It's worth re-checking the collimation & focus during a long session in case the cooling down has shifted things a little.

[alacant]

41 minutes ago, laser_jock99 said:

collimation & focus during a long session

Yeah, thanks. I'm still at a loss as to how I could remove and replace the camera with the same orientation. I learned the hard way; I thought that flats would be OK when taken with the camera lined up visually with the focus knobs at a later date...

** For the passive springs, I simply loosened the locking screws and placed the new springs over them. I see that you replaced the screws. Is there any disadvantage to my method? TIA.

[laser_jock99]

13 hours ago, alacant said:

 

** For the passive springs, I simply loosened the locking screws and placed the new springs over them. I see that you replaced the screws. Is there any disadvantage to my method? TIA.

As long as the passive springs don't shift or fall out- any method of holding them will work. I put  screws in just long enough hold the springs but too short to touch the mirror cell.

[alacant]

Hi. Here are the modifications. The collimation stays virtually unchanged between sessions. I haven't needed to adjust the secondary. It's the primary which may need aligning after a knock. HTH.

[alacant]

Could this be the final missing link? Running out of bits to tweak!

 

[laser_jock99]

On 13/03/2017 at 09:13, alacant said:

Could this be the final missing link? Running out of bits to tweak!

 

Anything that stops the mirror 'shifting' around while the scope moves between targets will help. Tighten the clips - but don't overtighten.

One thing I forgot to mention I did to the 250mm F4 Newtonian was add a thick foam band between the mirror cell and the steel tube. This was kill off any futher mirror cell 'slop' caused by using longer springs. It had the added bonus of blocking stray light coming up the tube. Probably wouldn't be a good idea if you have mirror cool down time issues (my scopes live outside in the cool obsy).

[alacant]

8 hours ago, laser_jock99 said:

Anything that stops the mirror 'shifting' around

Yeah. You can't assume anything. I thought the mirror would have been fixed correctly by either the factory or by ES. It was by accident I found out it was loose when adding the passive springs.

Maybe we need a checklist?