2 replies to this topic

[Phil49]

Hello,

 

I bought my Mak 180 second-hand a year ago.

 

I only use it for lunar photography, I'll see about planetary photography later.

 

Last year, during a session around April/May, I was able to use it with a Player One Marc C-II camera (IMX662) and I found the results quite good.

 

The weather since then, and the fact that I've been concentrating more on the deep sky, meant that I didn't start using my Mak again until a fortnight ago.

 

In the meantime, I ordered a new camera, another Player One, the Uranus C based on the excellent IMX585 (color and uncooled).

 

I made a few 60-second films, which were OK, and I also tried a Baader VIP Apo 2x barlow, but the results seemed catastrophic...

 

Finally, faced with these ‘mixed’ results, I checked the collimation by two means: with the Ocal, the control (I wait before making a modification) was very close to what the Ocal offered me visually, the cross was almost centred on the centre of the camera.

 

Finally, the day before yesterday, taking advantage of the last evening when I could see the moon from home, I defocused a star, and now I'm wondering about something!

 

Targeting a star, I then activated sidereal tracking and took out my Bahtinov mask to see if the focus was correct.

 

It was impossible to see the spikes, and the image obtained with the Mak in Firecapture was grainy.

 

I tried to play with gain, exposure time and fine focus with my EAF, but nothing worked.

 

I had a circle, yes, but with blurred edges and no spike, just a blurred star, and the star took on an oblong shape, which surprised me even more!

It was round again when I was reoving the focus mask!!

 

Is it normal not to be able to obtain a defocused ring like with one Ritchey Chretien (RC8)?

 

Is it normal not to be able to see spikes from a bahtinov mask?

 

Is this possible, but quite simply, despite the fact that the sky seemed clear, in altitude there may have been clouds that made the conditions ‘bad’ and prevented me from getting a decent result?

 

It's normal that I don't get the same results as my RC8, but without the benefit of hindsight and comparative images for these tests, I don't know what to think...

 

Thank you in advance for your help

 

Philippe

 

[JimFR]

A Bahtinov mask is strictly for focusing.  It’s going to trash the image itself, so whatever shape you see through it, I wouldn’t pay any attention to it.

 

As for the lack of spikes, this is tied to object brightness and clarity.  If the star is low on the horizon, it has many times more atmosphere to pass through than overhead regardless of how clear it looks.  Is there any issue with clarity and brightness of the mirrors and meniscus?  Any haze on the optical components are going to affect the image.

[Phil49]

Hello Jim,

 

Thks for your reply.

 

I know and pay much attention to the shape of stars through the bahtinov mask, but up to now I was more used to the shape through my newtons (a few years ago, as I sold it) and currently, through my RC8.

 

I know that we're not talking about the same kind of telescope, the bigger F/D can explain the lack of light, and the meniscus is different.

 

Yet when I use my bahtinov mask on both, and both have an obstruction, I clearly see a more or less round shape with my RC, even when I remove the mask, while with he Mak, I had almsotno spikes and the star was looking like a rugby ball when removing it!

 

My biggest doubt was the weather, because although the sky seemed clear, there might have been a light veil at altitude...

 

I'll try again next night, when the moon will again be visible from my observatory.

 

As for the height in the sky, admittedly I wasn't at the zenith, but I was targeting Mirfak, which isn't that low on the horizon ;-)

 

Philippe