21 hours ago, Chris33benoit said:

Nice picture of M8, beautiful.  Can I ask how many lights/darks/flats did you use for the Nebula?  Do we need equal amount of darks and lights ?  Thanks !

Thanks.

35 lights and IIRC, 20 flats and no darks were taken. Generally people only take around 30 darks. I think you should try with maybe more/less darks or even without them to stack with your raws to see how much it helps the image.

So I am planning to make a dew heater for my camera len using resistors wired in parallel, then distributing them around the circumference of the lens.

Diameter of lens: 65mm

Total power output: 6W

Power Supply(powerbank): 5V, 2A, 20Ah

Resistance for each resistor: 120 Ohm

Resistor power rating: 0.25W

Power output for each resistor: 0.21W

Current drawn: 1.21A

Number of resistor required: 29

Will probably insulate the wire with tape, and wrap the resistors in cloth around the lens. Is 6W too much or sufficient for this use? Any suggestions? Thanks.

Hi,

Yesterday a partial solar eclipse happened here so I took a few pictures using a DIY solar filter with the provided dust cap. And the center seems to have a blurry circle or reflection. Any idea? I don't remember this happening to the image when I use a full aperture filter which I wasn't using this time, was worried that it may fall off. Thanks.

Shot with SW150/750, ASI120MC and 2x Barlow.

Stacked on AutoStakkert!, edited on Registax and PS. Hold your phone away from you, it will look better😅

4 hours ago, symmetal said:

PHD2 will not dither without guiding, but APT has the option to dither without guiding. You need to select APT Dithering in the Guiding options. From the manual

Alan

Tried it, doesn't work. I selected the ZWO USBST4, the slew buttons just don't work. In PHD2 Manual Guide everything is okay as the option 'On Camera' is available. I guess EQDIRECT cable is necessary then.

I have seen a lot of questions about this topic but didn't get a clear answer. Is there a way that I can dither without guiding using APT and PHD2? I am using ST4 cable now and mounting a DSLR + kit lens on my EQ3 Pro to do normal sidereal tracking (maybe dithering is redundant at short focal length, say 24mm?)

Will disabling the RA and DEC corrections in PHD2 still allow dithering? Because I don't need guiding for the widefield setup and not planning to mount the guidescope on top either.

Thanks in advance.

Stars seem to 'travel' faster on the celestial equator than the stars situated at the poles. Why is this? Is this just a perspective problem?

I think if you want to avoid light pollution, travel to Mersing which I believe is close to your location.

Anyone done astrophotography with this guidescope? Sounds like a stupid idea, but being limited on budget, I was hoping to mount this on my EQ3 pro instead of the heavy Newtonian reflector. It costs only 120 dollars, a really cheap refractor. What do you think?

I am using a DSLR and only takes bias frames and flat frames but no darks as the temperature I believe doesn't match. I heard that if you already have bias frames or when the flats are of short exposures, you don't need dark flats. But IMO, usually dark flats aren't necessary. What do you think?

26 minutes ago, knobby said:

That's really come out well 👍 you could try more frames and then drizzle maybe ? Might be a bit bigger but I'd be very happy with that anyway !

Thanks for suggesting! I will try that later.

3 minutes ago, Uplooker said:

Congrats on a very good capture, well done. What equipment did you use?

Thanks! Skywatcher 150p with ASI120MC and 2x Barlow.

Stacked on AutoStakkert! and sharpened on Registax and PS. I wish I have access to a longer focal length to photograph this wonderful planet😁.

3 hours ago, alacant said:

Hi

I believe that on this forum, we're not allowed to use the terms fast and slow for anything other than motor vehicles!

If your target runs out of the field of view of the smaller sensor, you're going to have to move the camera and take more frames. Then combine them in software. That takes a long time. The large sensor get it all at once. No need to move the telescope and take more frames.

If your target fits into both the small and large sensors' field of view and the sensors are of equal sensitivity, then it takes the same time to build the image.

It doesn't matter what focal ratio you use. The only way you can get the image in less time in the latter case is to use a larger aperture telescope.

Sometimes theory and explanation just don't help.

When you've seen it first hand, you get it immediately. I too needed convincing. Try a side by side on the same target with a large and a small telescope. e.g. 80mm and 130mm. Markarian's Chain is a good target . Do 5 minute exposures in each. You'll not need telling which image is taken with which.

Same exercise with a large and a small sensor, but same telescope. The whole of Markarian's Chain fits into one frame with a large sensor but you'd need say 2 frames to cover the same area of sky with a small sensor. Try with a 183 and a dslr.

56 minutes ago, vlaiv said:

It is faster in one particular example - trying to get larger FOV than small sensor is capable of.

In this case you are limited (we exclude focal reducers for the time being or we assume that it is already fitted in form of CC / FF) to mosaic technique. Imagine that you have to take 4 panels to cover target with small sensor.

Large sensor will cover all of that in one go - let's say one hour. To get hour worth of signal per panel - you need to spend 4h total to get the same image with smaller sensor.

Ah, I think I misunderstood the term "faster" here, I related it to the light gathering ability of the camera, light gathering ability as in like, for example, we have one deep sky object that both the sensor can capture completely, now we crop it to the same size so both images show the same features of the DSO, so the SNR for both of them will be the same, therefore for different sensor size using the same focal ratio scope, how fast they collect light is the same. I agree the larger sensor covers wider FOV whereas smaller sensor covers smaller FOV and larger sensor is faster, in another way, that they will cover bigger area of the sky and the total light collected will be greater. Thanks for clarifying, I hope that I didn't confuse myself again.

9 hours ago, vlaiv said:

Alternatively, you can use large sensor on large scope and get faster system. Large sensor is going to be faster if matched with proper scope compared to small sensor.

 

Using the same scope but with two different sensors size, why would the combination with bigger sensor be faster when they have the same focal ratio? Please correct me if I misunderstood this.

8 hours ago, steppenwolf said:

You might like to have a look at 'Scientific Astrophotography' by Gerald H Hubbell. For what it is worth, this is my personal synopsis of the book:-

Hubbell’s background as a Nuclear Instrumentation and Controls Engineer shows through in the writing style of this book as it is unlike any other book you will have read on the subject of Astrophotography.

Hubbell introduces the reader to a whole host of new acronyms, some of his own making and these make for rather tiresome reading after a while. These and the general writing style read more like an in-depth functional specification document on the subject of astrophotography than typical books on the subject. Unfortunately, this gives the book a rather cold feel but it is well worth persevering as useful and, more importantly, accurate information is hidden within the text of the ‘observation program’ that he is training you to develop.

Subjects covered include equipment choice, integration of the equipment, image acquisition and calibration, scientific image data analysis, how to submit your data to scientific organisations and the use of professional level observatories for image capture.

As the title suggests, the book is not intended to guide you through the process of capturing and processing ‘pretty picture’ astrophotographs but rather how to take images suitable for astrometric, photometric and spectroscopic analysis. The text is fairly heavy on mathematics but the calculations serve to underline the scientific endeavour that the book seeks to teach.

The ‘functional specification’ writing style is both the book’s strength and its weakness – while many readers will see it as underpinning the scientific credentials of the work, others may simply find it just too hard-going.

 

Thanks for writing the summary, Steve. I will have a look at the book. Looking forward to your zoom meeting later at 3am as well 😁

Hello all,

Any good books or websites out there about theories of astrophotography? Things such as SNR, types of noise... would be great. 

Hello all,

Recently I have been thinking to implement dithering to my mount to remove walking noise, but my mount has a declination backlash, around 3 seconds or less. So is it okay to disable the dec guiding, and let APT and PHD2 dither in RA? I have heard that this will introduce more noise to my DSLR images. Another solution is to try measuring backlash in guiding assistant and guide in both dec directions, will it give good dither results under backlash compensation in PHD2? What do you think?

In manual focus, the focus ring might shift a bit when I am shooting widefield images and taking flat frames, is there a way to lock the focus ring? Thanks.

35 x 1 minute of Lagoon Nebula under Bortle 8 skies taken with stock D5300, SW150/750 and EQ3 Pro. Had to say the gradient in the image was really bad because of the lazy and forgetful me that took the flats in a different camera orientation plus the possibilities of light leaking into the setup. Thanks to @alacant for giving the advice on stacking and AstroBackyard's Astrophotography Tutorial: How to Remove Gradients in Photoshop. Although the way of removing the gradient seems extremely unusual to me, but it works! I believe a lot of the advanced softwares like Pixinsight or plugins such as GradientXTerminator would solve the problem very easily.

1 hour ago, alacant said:

Hi

Looks good. Why not stack with the flat frames too? Then you'd have even illumination. 

If you want to lose the coma, you'll have to use a coma corrector.

Is this the 150/750? If so, the collimation looks correctly offset. 

Make a master bias from say 50 or so frames. Subtract this from each of the flat and light frames before stacking. Most apps which do stacking will do this calibration for you. 

Use a black shower cap over the primary mirror end of the tube and tape over the camera viewfinder.

HTH

Alright, took 50 bias frames just now and got this. I just won't learn from my mistakes lol, I took the flats with a slightly different camera orientation as I removed it before the next session... This is probably why the image has a linear gradient across I think.  The overall gradient looks slightly better compared to the ones uncalibrated and with flats only, in my opinion.

Yep, this is a Skywatcher 150p.

I just loaded all the bias and flat frames into DSS and let it do its job. I think that's ok too?

Great idea! I will get a shower cap then. Thanks a lot.

biasflatm6.TIF

Hello all, here to ask about uneven field vignetting and whether it is caused by collimation or not.  Attached are pictures of a single raw flat, then the same flat applied with contrast adjustment, telescope's collimation, lagoon nebula stacked of 37x1 minute subs consisting of just light frames. I found that the coma in the field has been getting worse that they started showing so early, close to the center of the image. I was wondering whether this is normal or just because of my bad collimation, but collimation looks fine in the attached picture with everything centered. And the flat as well, it looks darker on the left side, I think this might be due to camera or adapters tilting a bit, or even collimation again? I thought about light leak in the scope, but it does not seem be the problem. But still, I did some light leak test because of the unending, annoying gradient in the picture, by shining my phone's flashlight on the primary mirror, and there's light leak! So in the next imaging session I will try to cover the mirror and also my DSLR's viewfinder as I am imaging near a streetlight.

I have also heard that without bias frames, flat frames wouldn't work well when calibrated to the lights. 

Thanks in advance and clear skies.

7 minutes ago, Merlin66 said:

I use a Starlight Lodestar for guiding my NEQ6pro mount and ST-4 connections and EQMod.

The Aux in PHD needs to be set to "EQmod ASCOM HEQ5/6" - this then allows PHD to access the RA and Dec of the target object.

Hope this helps.

 

I thought EQMOD only works when you have a EQDirect cable? I have been selecting 'None' in the previous sessions. So I have to install EQMOD as well right? The ASCOM drivers are installed as I am using ASI120MC to guide.

I am currently using a ST4 cable to guide, so do I need to select anything under the Aux Mount selections? There is a 'ZWO USBST4 ASCOM' option.

Just to confirm, when shooting from APT, I always close the flipping screen of the camera. Is this the correct way?

Sorry for using this thread.