Pitch Black Skies

In the middle of flocking inside the OTA. It's definitely a lot darker in there. Whether it will make any difference to the contrast in my images is another matter 🤷

Oh well,

Nothing Ventured, Nothing Gained.

Do you still not put anything over the primary end Adam? Just wondering if it's really necessary. Congrats on NASA APOD! That's a fantastic achievement.

22 minutes ago, BrendanC said:

Yes. I've tried putting the ASI1600 below the OTA but it doesn't work with the rings and auto focuser. Everything balances fine, and as far as I can tell I'm not getting any focuser slop. Why?

No it's not that. I can see that the primary end is exposed. The 130P-DS's have serious light leaks at the primary end and I'm wondering if that could be the cause of your problems. If you look down the tube through the 50mm aperture on the dust cap while moving a torch around the primary you should see light beaming through the edges. A rubber swimming hat or a shower cap placed over the primary end completely rectifies it.

Brendan, you don't happen to image with your set up exactly like this do you?

https://www.firstlightoptics.com/offers/offer_skywatcher-explorer-130p-ds-ota_307251.html

I'm trying to calculate my 130P-DS's true focal ratio.

It's labelled as F5 but I'm trying to calculate how much of the secondary mirror is blocking the primary.

The secondary's minor axis is believed to be 47mm. I presume this means the diameter of circle when tilted at 45°?

The primary's diameter is 130mm.

Do I find the area of each circle then divide one into the other?

A warm welcome to SGL

Thank you @Grierson, you have been a pleasure to deal with.

Items packaged very securely and in excellent condition. Some of these bags have never even been opened..

1 hour ago, ONIKKINEN said:

Is this really the case? I thought the focal length comes from the shape of the mirror itself and pushing the mirror up will just push the focal point up (and perhaps cause extra vignetting).

Yeah you're right mate sorry, don't know what I was thinking there.

21 minutes ago, alacant said:

The focal length remains exactly the same. This is not the reason the f ratio changes. 

My bad, you're right. 

A Newtonian's focal length is measured from the distance of the primary to the secondary, PLUS the distance from the secondary to the point of focus 🙂

By pushing the primary up, we are also pushing the point of focus up so in fact the focal length remains exactly the same.

42 minutes ago, Bibabutzemann said:

Wouldnt you need an adational adapter to reach the 55mm distance between MPCC and sensor with that 1mm adapter?

That's what I was thinking too. It just subtracts from the backfocus. The cc position doesn't change by using 1mm adapter. 

2 hours ago, alacant said:

Given that you'll no longer be using the full diameter of the primary mirror, yes. Bear in mind however that a 130mm mirror with a fl of 650mm will always be f5.

The main disadvantage is that if you move the primary mirror 20mm up the tube, the standard issue secondary will not intercept all the light the primary offers. Visually imperceptible. Imaging wise, losing valuable light; imagers need every microgram of light they can possibly muster;)

Indeed, but if the primary is pushed up 20mm it shortens the focal length to 630mm.

630/130 = 4.85 focal ratio.

I don't believe this shorter focal ratio helps gather light quicker, as you have already mentioned that now all of the light isn't incepted by the standard secondary.

Still not convinced it would make a drastic difference though 🙂

Definitely worth trying if anything.

23 minutes ago, edarter said:

They add 1mm to the image train rather than the normal 11mm.

Is that 10mm not coming out of your backfocus?

With a normal T ring you can achieve focus too by just using longer screws. No need to get the low profile one.

On an older scope I just replaced the factory screws with ones that were 20mm longer. Using this method reduces the focal ratio of your scope but I've heard it can also reduce the amount of reflected light on to the secondary. A larger secondary would probably solve it, but then you are reducing the amount of light that hits the primary 🤪

Personally, I couldn't notice any difference with just using longer screws, but it worried me that I messed with focal ratio so opted for chopping the tube in the end.

I'd advise just try using longer screws and see what happens. If it has an obvious negative impact on your images you can easily change back and it has only cost you a couple of pounds. I think you might be pleasantly surprised.

16 minutes ago, alacant said:

The earlier European ones, yes. Proper GPUs come with a graph showing the relation between focal length and backfocus and have a chart showing recommended positions for various focal lengths. Beware modem mass produced copies.

This for example is a proper GPU which will give corner to corner over APS-c.

This, although it may still work up to a point, isn't but still way better than the 2 element correctors.

Cheers 

 

 

All this time I have been gutted about buying the Skywatcher Aplanatic instead of the GPU with the brass collar.

Are you saying my Aplanatic is the same as the proper GPU? 😮

I noticed the flange doesn't unthread on the proper GPU just like my Aplanatic. That's really the reason why I wanted the GPU with the brass collar. It can be threaded onto the focuser tube. Do you think that is an advantage or not really necessary? I can see how camera rotation could be a problem.

Cheers 

P.S. there is a Skywatcher Aplanatic for sale in the classifieds section 🙂

The Aplanatic is another excellent corrector. It looks the same as GPU but it is different. 

- The Aplanatic can't be threaded onto the focuser tube like the GPU can.

- The Aplanatic pushes the focus position out by 6mm. (You will still have a protruding tube in the light path).

- The GPU pushes the focus position out by 19mm.

Can't really comment on the Maxfield but @ONIKKINEN 's experience with it turned me off buying it. Maybe that was just a bad example?

If you can at all, get the GPU. Excellent correction and hassle free.

It pushes the focus position out by 19mm so no need to chop the end of the tube.

It has another really neat advantage too in that it can be screwed into the focuser tube for extra stability and security.

A bit of an odd one here but something that has interested me.

Has anyone here ever taken a picture of a rainbow with their full spectrum camera?

Just wondering how it would look, and if the UV and IR are visible.

@Richard Wesson I have one if you'd like to buy it. I paid €36 for it from astroshop.eu.

PM me for further details.

With thanks to @markse68

In mint condition, packaged securely, and posted promptly.

2" Concenter

Hi guys,

For anyone that has cut their focuser tube, I have come up with a little mod to stop the tube from coming off the rollers when racking all of the way out.

I attached a small washer on the tube's track with some metal compound.

We now have a low profile focuser ✊

It doesn't look great but don't worry as it's completely hidden.

Depending on where you have cut your tube and what type of coma corrector you use will determine where the washer needs to be placed.

You can check this easily with the focuser removed from the telescope.

I've just tested guiding with the new bearings. I'm now averaging around .60 total RMS.

At one stage I was going steady at .37!

Huge improvement.

Just to note, it did take some tweaking and fine adjustments even after the new bearings were installed.

The 1s exp is the main cam. The guide cam was set at 2s exp.

5 minutes ago, starwatcher_ch said:

Looks great! Well done.

Agreed, really tidy job 👏

2 hours ago, alacant said:

would you recommend this method?

Hey,

I think for my mount, I could have just gotten away with replacing the worm carrier bearings. All of the others seemed fine. I have seen someone on YouTube complain about the their HEQ5's worm carrier bearings too. I don't think they are the best quality.

Something I have learned about bearings too from this is that the 2RS in the model number stands for 2 rubber seals. They're assumed superior to the zz or 2z.

"What is the difference between 2RS and ZZ bearings? The 2RS are sealed for life bearings i.e. the grease within the bearing cannot get out or contaminants get into the bearing and damage it. The ZZ are just a metal shield to stop larger contaminants damaging the bearing."

I think your method is fine, especially for a business. A full strip down, re-grease and all bearings replaced gives peace of mind to both yourself and the customer, and it rules out any potential problems if guiding errors still persist.

I think the clean and re-grease is important and while that's being done it doesn't take a whole lot to swap out the bearings too.

If you are finding it too demanding though, it might be interesting to trial just replacing the worm carrier ones.

Or even better, get me a flight over.. I could do with a few days in the 🌞

😅

Cheers

9 hours ago, vlaiv said:

you are already over sampling with 2.4um pixel size

How do you calculate this vlaiv?

I know you have issues with the credibility of this calculator but I always use it as I don't know any better.

This is what I get when using it;