2019-06-01+Sky+and+Telescope

72 JUNE 2019 • SKY & TELESCOPE

S&T Test Report

bytes for a 30-second clip made with

a small region of interest. The manual

does warn about this, but it was still an

eye opener to fi ll more than 50 giga-

bytes of disk space recording about a

dozen video clips my fi rst night out.

These videos were later processed with

third-party software including RegiStax

and the freeware AutoStakkert!3.

On to the Deep Sky

Once the Moon was out of the eve-

ning sky it was time to try the DSI-IV

for deep-sky imaging. It’s here where

I found room for improvement with

SkyCapture that I hadn’t noticed when

shooting still images during my bench

testing in a relatively bright environ-

ment. For example, when framing faint

deep-sky targets, I usually make short

exposures of 20 to 60 seconds and

stretch them to extremes to see what’s

in the fi eld. With SkyCapture, the image

that appears at the end of each expo-

sure can’t be stretched on screen as is.

You can examine a histogram of the

displayed image and make adjustments

to set the black and white points for

displaying a stretched image, but these

settings do not take effect until you

make the next exposure.

The best workaround, apart from

making multiple exposures or guessing

at the correct histogram settings before

shooting the fi rst one (something that

is possible with experience), is to fi rst

save the image and then re-open it with

SkyCapture and use the Range function

in the Process menu to actively stretch

the image on screen. It’s a bit clumsy,

not to mention time-consuming, espe-

cially if you’re typing fi le names and the

like in the dark with gloves on.

There were also features of the

software that I couldn’t get to work,

including the automatic functions for

dark-frame subtraction and fl at-fi eld

correction. These issues may be unique

to the DSI-IV update of the software,

since I noticed that the

fl at-fi eld function isn’t

even discussed in the

older user’s manual

that I mentioned ear-

lier. Regardless, I don’t

like using automatic

calibration routines

during image capture,

since I prefer having

unmodifi ed raw data

that can be processed

later with various

calibration methods. As

such, I simply made standard dark and

fl at-fi eld exposures with the DSI-IV and

processed my light frames with third-

party software.

Despite my nit-picks with SkyCap-

ture, I did use the software exclusively

for all the imaging I did with the

DSI-IV, and I’m happy with my results.

Indeed, most astronomical cameras

come with only the most rudimentary

image-capture software (and some don’t

come with any), so getting a package as

decent as SkyCapture included with the

purchase of the DSI-IV is really a plus.

In the end I found the DSI-IV to

be a very versatile camera that can

satisfy the needs of many of today’s

astroimagers. It’s a camera that can

shoot excellent astronomical video and

seamlessly transition to shooting decent

long-exposure deep-sky images. It can’t

quite match the deep-sky performance

of a cooled, 16-bit, astronomical CCD

camera, but the DSI-IV is still a big step

up from the astrophotography that can

be done with DSLRs. And it comes with

a very attractive price tag, especially

given the software that’s included.

■DENNIS DI CICCO has been reviewing

astronomical equipment in the pages of

Sky & Telescope for more than 45 years.

pSwitching the DSI-IV from shooting astronomical videos to making long exposures of deep-sky

objects involves only a few mouse clicks with the camera’s included Meade SkyCapture software

and, for optimum results, connecting the 12-volt power supply for the cooling system. These

views of the Cone Nebula and Christmas Tree Cluster in Monoceros (left) and Horsehead Nebula

in Orion (right) were each assembled from fi fteen 10-minute exposures through a hydrogen-alpha

fi lter with an 8-inch f/3 telescope.

qDuring his testing, the author exclusively

used the SkyCapture software supplied with

the DSI-IV for his astronomical imaging. As

explained in the accompanying text, he feels

the software’s long-exposure mode could

stand some improvement but was still effective

for capturing images. The screen grab seen

here displays one of the 10-minute exposures

used for the image above and was made while

the camera was in the process of running the

automated exposure sequence.